linux/kernel/debug/debug_core.c

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/*
* Kernel Debug Core
*
* Maintainer: Jason Wessel <jason.wessel@windriver.com>
*
* Copyright (C) 2000-2001 VERITAS Software Corporation.
* Copyright (C) 2002-2004 Timesys Corporation
* Copyright (C) 2003-2004 Amit S. Kale <amitkale@linsyssoft.com>
* Copyright (C) 2004 Pavel Machek <pavel@ucw.cz>
* Copyright (C) 2004-2006 Tom Rini <trini@kernel.crashing.org>
* Copyright (C) 2004-2006 LinSysSoft Technologies Pvt. Ltd.
* Copyright (C) 2005-2009 Wind River Systems, Inc.
* Copyright (C) 2007 MontaVista Software, Inc.
* Copyright (C) 2008 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Contributors at various stages not listed above:
* Jason Wessel ( jason.wessel@windriver.com )
* George Anzinger <george@mvista.com>
* Anurekh Saxena (anurekh.saxena@timesys.com)
* Lake Stevens Instrument Division (Glenn Engel)
* Jim Kingdon, Cygnus Support.
*
* Original KGDB stub: David Grothe <dave@gcom.com>,
* Tigran Aivazian <tigran@sco.com>
*
* This file is licensed under the terms of the GNU General Public License
* version 2. This program is licensed "as is" without any warranty of any
* kind, whether express or implied.
*/
#include <linux/pid_namespace.h>
#include <linux/clocksource.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/console.h>
#include <linux/threads.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/sched.h>
#include <linux/sysrq.h>
#include <linux/init.h>
#include <linux/kgdb.h>
#include <linux/kdb.h>
#include <linux/pid.h>
#include <linux/smp.h>
#include <linux/mm.h>
#include <linux/rcupdate.h>
#include <asm/cacheflush.h>
#include <asm/byteorder.h>
#include <linux/atomic.h>
#include <asm/system.h>
#include "debug_core.h"
static int kgdb_break_asap;
struct debuggerinfo_struct kgdb_info[NR_CPUS];
/**
* kgdb_connected - Is a host GDB connected to us?
*/
int kgdb_connected;
EXPORT_SYMBOL_GPL(kgdb_connected);
/* All the KGDB handlers are installed */
int kgdb_io_module_registered;
/* Guard for recursive entry */
static int exception_level;
struct kgdb_io *dbg_io_ops;
static DEFINE_SPINLOCK(kgdb_registration_lock);
/* kgdb console driver is loaded */
static int kgdb_con_registered;
/* determine if kgdb console output should be used */
static int kgdb_use_con;
/* Flag for alternate operations for early debugging */
bool dbg_is_early = true;
/* Next cpu to become the master debug core */
int dbg_switch_cpu;
/* Use kdb or gdbserver mode */
int dbg_kdb_mode = 1;
static int __init opt_kgdb_con(char *str)
{
kgdb_use_con = 1;
return 0;
}
early_param("kgdbcon", opt_kgdb_con);
module_param(kgdb_use_con, int, 0644);
/*
* Holds information about breakpoints in a kernel. These breakpoints are
* added and removed by gdb.
*/
static struct kgdb_bkpt kgdb_break[KGDB_MAX_BREAKPOINTS] = {
[0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED }
};
/*
* The CPU# of the active CPU, or -1 if none:
*/
atomic_t kgdb_active = ATOMIC_INIT(-1);
EXPORT_SYMBOL_GPL(kgdb_active);
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
static DEFINE_RAW_SPINLOCK(dbg_master_lock);
static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
/*
* We use NR_CPUs not PERCPU, in case kgdb is used to debug early
* bootup code (which might not have percpu set up yet):
*/
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
static atomic_t masters_in_kgdb;
static atomic_t slaves_in_kgdb;
static atomic_t kgdb_break_tasklet_var;
atomic_t kgdb_setting_breakpoint;
struct task_struct *kgdb_usethread;
struct task_struct *kgdb_contthread;
int kgdb_single_step;
static pid_t kgdb_sstep_pid;
/* to keep track of the CPU which is doing the single stepping*/
atomic_t kgdb_cpu_doing_single_step = ATOMIC_INIT(-1);
/*
* If you are debugging a problem where roundup (the collection of
* all other CPUs) is a problem [this should be extremely rare],
* then use the nokgdbroundup option to avoid roundup. In that case
* the other CPUs might interfere with your debugging context, so
* use this with care:
*/
kgdb: fix signedness mixmatches, add statics, add declaration to header Noticed by sparse: arch/x86/kernel/kgdb.c:556:15: warning: symbol 'kgdb_arch_pc' was not declared. Should it be static? kernel/kgdb.c:149:8: warning: symbol 'kgdb_do_roundup' was not declared. Should it be static? kernel/kgdb.c:193:22: warning: symbol 'kgdb_arch_pc' was not declared. Should it be static? kernel/kgdb.c:712:5: warning: symbol 'remove_all_break' was not declared. Should it be static? Related to kgdb_hex2long: arch/x86/kernel/kgdb.c:371:28: warning: incorrect type in argument 2 (different signedness) arch/x86/kernel/kgdb.c:371:28: expected long *long_val arch/x86/kernel/kgdb.c:371:28: got unsigned long *<noident> kernel/kgdb.c:469:27: warning: incorrect type in argument 2 (different signedness) kernel/kgdb.c:469:27: expected long *long_val kernel/kgdb.c:469:27: got unsigned long *<noident> kernel/kgdb.c:470:27: warning: incorrect type in argument 2 (different signedness) kernel/kgdb.c:470:27: expected long *long_val kernel/kgdb.c:470:27: got unsigned long *<noident> kernel/kgdb.c:894:27: warning: incorrect type in argument 2 (different signedness) kernel/kgdb.c:894:27: expected long *long_val kernel/kgdb.c:894:27: got unsigned long *<noident> kernel/kgdb.c:895:27: warning: incorrect type in argument 2 (different signedness) kernel/kgdb.c:895:27: expected long *long_val kernel/kgdb.c:895:27: got unsigned long *<noident> kernel/kgdb.c:1127:28: warning: incorrect type in argument 2 (different signedness) kernel/kgdb.c:1127:28: expected long *long_val kernel/kgdb.c:1127:28: got unsigned long *<noident> kernel/kgdb.c:1132:25: warning: incorrect type in argument 2 (different signedness) kernel/kgdb.c:1132:25: expected long *long_val kernel/kgdb.c:1132:25: got unsigned long *<noident> Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com> Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
2008-04-24 21:57:23 +00:00
static int kgdb_do_roundup = 1;
static int __init opt_nokgdbroundup(char *str)
{
kgdb_do_roundup = 0;
return 0;
}
early_param("nokgdbroundup", opt_nokgdbroundup);
/*
* Finally, some KGDB code :-)
*/
/*
* Weak aliases for breakpoint management,
* can be overriden by architectures when needed:
*/
int __weak kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr)
{
int err;
err = probe_kernel_read(saved_instr, (char *)addr, BREAK_INSTR_SIZE);
if (err)
return err;
return probe_kernel_write((char *)addr, arch_kgdb_ops.gdb_bpt_instr,
BREAK_INSTR_SIZE);
}
int __weak kgdb_arch_remove_breakpoint(unsigned long addr, char *bundle)
{
return probe_kernel_write((char *)addr,
(char *)bundle, BREAK_INSTR_SIZE);
}
int __weak kgdb_validate_break_address(unsigned long addr)
{
char tmp_variable[BREAK_INSTR_SIZE];
int err;
/* Validate setting the breakpoint and then removing it. In the
* remove fails, the kernel needs to emit a bad message because we
* are deep trouble not being able to put things back the way we
* found them.
*/
err = kgdb_arch_set_breakpoint(addr, tmp_variable);
if (err)
return err;
err = kgdb_arch_remove_breakpoint(addr, tmp_variable);
if (err)
printk(KERN_ERR "KGDB: Critical breakpoint error, kernel "
"memory destroyed at: %lx", addr);
return err;
}
unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs)
{
return instruction_pointer(regs);
}
int __weak kgdb_arch_init(void)
{
return 0;
}
int __weak kgdb_skipexception(int exception, struct pt_regs *regs)
{
return 0;
}
/*
* Some architectures need cache flushes when we set/clear a
* breakpoint:
*/
static void kgdb_flush_swbreak_addr(unsigned long addr)
{
if (!CACHE_FLUSH_IS_SAFE)
return;
if (current->mm && current->mm->mmap_cache) {
flush_cache_range(current->mm->mmap_cache,
addr, addr + BREAK_INSTR_SIZE);
}
/* Force flush instruction cache if it was outside the mm */
flush_icache_range(addr, addr + BREAK_INSTR_SIZE);
}
/*
* SW breakpoint management:
*/
int dbg_activate_sw_breakpoints(void)
{
unsigned long addr;
int error;
int ret = 0;
int i;
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if (kgdb_break[i].state != BP_SET)
continue;
addr = kgdb_break[i].bpt_addr;
error = kgdb_arch_set_breakpoint(addr,
kgdb_break[i].saved_instr);
if (error) {
ret = error;
printk(KERN_INFO "KGDB: BP install failed: %lx", addr);
continue;
}
kgdb_flush_swbreak_addr(addr);
kgdb_break[i].state = BP_ACTIVE;
}
return ret;
}
int dbg_set_sw_break(unsigned long addr)
{
int err = kgdb_validate_break_address(addr);
int breakno = -1;
int i;
if (err)
return err;
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if ((kgdb_break[i].state == BP_SET) &&
(kgdb_break[i].bpt_addr == addr))
return -EEXIST;
}
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if (kgdb_break[i].state == BP_REMOVED &&
kgdb_break[i].bpt_addr == addr) {
breakno = i;
break;
}
}
if (breakno == -1) {
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if (kgdb_break[i].state == BP_UNDEFINED) {
breakno = i;
break;
}
}
}
if (breakno == -1)
return -E2BIG;
kgdb_break[breakno].state = BP_SET;
kgdb_break[breakno].type = BP_BREAKPOINT;
kgdb_break[breakno].bpt_addr = addr;
return 0;
}
int dbg_deactivate_sw_breakpoints(void)
{
unsigned long addr;
int error;
int ret = 0;
int i;
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if (kgdb_break[i].state != BP_ACTIVE)
continue;
addr = kgdb_break[i].bpt_addr;
error = kgdb_arch_remove_breakpoint(addr,
kgdb_break[i].saved_instr);
if (error) {
printk(KERN_INFO "KGDB: BP remove failed: %lx\n", addr);
ret = error;
}
kgdb_flush_swbreak_addr(addr);
kgdb_break[i].state = BP_SET;
}
return ret;
}
int dbg_remove_sw_break(unsigned long addr)
{
int i;
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if ((kgdb_break[i].state == BP_SET) &&
(kgdb_break[i].bpt_addr == addr)) {
kgdb_break[i].state = BP_REMOVED;
return 0;
}
}
return -ENOENT;
}
int kgdb_isremovedbreak(unsigned long addr)
{
int i;
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if ((kgdb_break[i].state == BP_REMOVED) &&
(kgdb_break[i].bpt_addr == addr))
return 1;
}
return 0;
}
int dbg_remove_all_break(void)
{
unsigned long addr;
int error;
int i;
/* Clear memory breakpoints. */
for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) {
if (kgdb_break[i].state != BP_ACTIVE)
goto setundefined;
addr = kgdb_break[i].bpt_addr;
error = kgdb_arch_remove_breakpoint(addr,
kgdb_break[i].saved_instr);
if (error)
printk(KERN_ERR "KGDB: breakpoint remove failed: %lx\n",
addr);
setundefined:
kgdb_break[i].state = BP_UNDEFINED;
}
/* Clear hardware breakpoints. */
if (arch_kgdb_ops.remove_all_hw_break)
arch_kgdb_ops.remove_all_hw_break();
return 0;
}
/*
* Return true if there is a valid kgdb I/O module. Also if no
* debugger is attached a message can be printed to the console about
* waiting for the debugger to attach.
*
* The print_wait argument is only to be true when called from inside
* the core kgdb_handle_exception, because it will wait for the
* debugger to attach.
*/
static int kgdb_io_ready(int print_wait)
{
if (!dbg_io_ops)
return 0;
if (kgdb_connected)
return 1;
if (atomic_read(&kgdb_setting_breakpoint))
return 1;
if (print_wait) {
#ifdef CONFIG_KGDB_KDB
if (!dbg_kdb_mode)
printk(KERN_CRIT "KGDB: waiting... or $3#33 for KDB\n");
#else
printk(KERN_CRIT "KGDB: Waiting for remote debugger\n");
#endif
}
return 1;
}
static int kgdb_reenter_check(struct kgdb_state *ks)
{
unsigned long addr;
if (atomic_read(&kgdb_active) != raw_smp_processor_id())
return 0;
/* Panic on recursive debugger calls: */
exception_level++;
addr = kgdb_arch_pc(ks->ex_vector, ks->linux_regs);
dbg_deactivate_sw_breakpoints();
/*
* If the break point removed ok at the place exception
* occurred, try to recover and print a warning to the end
* user because the user planted a breakpoint in a place that
* KGDB needs in order to function.
*/
if (dbg_remove_sw_break(addr) == 0) {
exception_level = 0;
kgdb_skipexception(ks->ex_vector, ks->linux_regs);
dbg_activate_sw_breakpoints();
printk(KERN_CRIT "KGDB: re-enter error: breakpoint removed %lx\n",
addr);
WARN_ON_ONCE(1);
return 1;
}
dbg_remove_all_break();
kgdb_skipexception(ks->ex_vector, ks->linux_regs);
if (exception_level > 1) {
dump_stack();
panic("Recursive entry to debugger");
}
printk(KERN_CRIT "KGDB: re-enter exception: ALL breakpoints killed\n");
#ifdef CONFIG_KGDB_KDB
/* Allow kdb to debug itself one level */
return 0;
#endif
dump_stack();
panic("Recursive entry to debugger");
return 1;
}
static void dbg_touch_watchdogs(void)
{
touch_softlockup_watchdog_sync();
clocksource_touch_watchdog();
rcu_cpu_stall_reset();
}
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
int exception_state)
{
unsigned long flags;
int sstep_tries = 100;
int error;
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
int cpu;
int trace_on = 0;
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
int online_cpus = num_online_cpus();
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
kgdb_info[ks->cpu].enter_kgdb++;
kgdb_info[ks->cpu].exception_state |= exception_state;
if (exception_state == DCPU_WANT_MASTER)
atomic_inc(&masters_in_kgdb);
else
atomic_inc(&slaves_in_kgdb);
if (arch_kgdb_ops.disable_hw_break)
arch_kgdb_ops.disable_hw_break(regs);
acquirelock:
/*
* Interrupts will be restored by the 'trap return' code, except when
* single stepping.
*/
local_irq_save(flags);
cpu = ks->cpu;
kgdb_info[cpu].debuggerinfo = regs;
kgdb_info[cpu].task = current;
kgdb_info[cpu].ret_state = 0;
kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
/* Make sure the above info reaches the primary CPU */
smp_mb();
if (exception_level == 1) {
if (raw_spin_trylock(&dbg_master_lock))
atomic_xchg(&kgdb_active, cpu);
goto cpu_master_loop;
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
}
/*
* CPU will loop if it is a slave or request to become a kgdb
* master cpu and acquire the kgdb_active lock:
*/
while (1) {
cpu_loop:
if (kgdb_info[cpu].exception_state & DCPU_NEXT_MASTER) {
kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
goto cpu_master_loop;
} else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
if (raw_spin_trylock(&dbg_master_lock)) {
atomic_xchg(&kgdb_active, cpu);
break;
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
}
} else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
if (!raw_spin_is_locked(&dbg_slave_lock))
goto return_normal;
} else {
return_normal:
/* Return to normal operation by executing any
* hw breakpoint fixup.
*/
if (arch_kgdb_ops.correct_hw_break)
arch_kgdb_ops.correct_hw_break();
if (trace_on)
tracing_on();
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
kgdb_info[cpu].exception_state &=
~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
kgdb_info[cpu].enter_kgdb--;
smp_mb__before_atomic_dec();
atomic_dec(&slaves_in_kgdb);
dbg_touch_watchdogs();
local_irq_restore(flags);
return 0;
}
cpu_relax();
}
/*
* For single stepping, try to only enter on the processor
* that was single stepping. To guard against a deadlock, the
* kernel will only try for the value of sstep_tries before
* giving up and continuing on.
*/
if (atomic_read(&kgdb_cpu_doing_single_step) != -1 &&
(kgdb_info[cpu].task &&
kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
atomic_set(&kgdb_active, -1);
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
raw_spin_unlock(&dbg_master_lock);
dbg_touch_watchdogs();
local_irq_restore(flags);
goto acquirelock;
}
if (!kgdb_io_ready(1)) {
kgdb_info[cpu].ret_state = 1;
goto kgdb_restore; /* No I/O connection, resume the system */
}
/*
* Don't enter if we have hit a removed breakpoint.
*/
if (kgdb_skipexception(ks->ex_vector, ks->linux_regs))
goto kgdb_restore;
/* Call the I/O driver's pre_exception routine */
if (dbg_io_ops->pre_exception)
dbg_io_ops->pre_exception();
/*
* Get the passive CPU lock which will hold all the non-primary
* CPU in a spin state while the debugger is active
*/
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
if (!kgdb_single_step)
raw_spin_lock(&dbg_slave_lock);
#ifdef CONFIG_SMP
/* Signal the other CPUs to enter kgdb_wait() */
if ((!kgdb_single_step) && kgdb_do_roundup)
kgdb_roundup_cpus(flags);
#endif
/*
* Wait for the other CPUs to be notified and be waiting for us:
*/
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
atomic_read(&slaves_in_kgdb)) != online_cpus)
cpu_relax();
/*
* At this point the primary processor is completely
* in the debugger and all secondary CPUs are quiescent
*/
dbg_deactivate_sw_breakpoints();
kgdb_single_step = 0;
kgdb_contthread = current;
exception_level = 0;
trace_on = tracing_is_on();
if (trace_on)
tracing_off();
while (1) {
cpu_master_loop:
if (dbg_kdb_mode) {
kgdb_connected = 1;
error = kdb_stub(ks);
if (error == -1)
continue;
kgdb_connected = 0;
} else {
error = gdb_serial_stub(ks);
}
if (error == DBG_PASS_EVENT) {
dbg_kdb_mode = !dbg_kdb_mode;
} else if (error == DBG_SWITCH_CPU_EVENT) {
kgdb_info[dbg_switch_cpu].exception_state |=
DCPU_NEXT_MASTER;
goto cpu_loop;
} else {
kgdb_info[cpu].ret_state = error;
break;
}
}
/* Call the I/O driver's post_exception routine */
if (dbg_io_ops->post_exception)
dbg_io_ops->post_exception();
if (!kgdb_single_step) {
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
raw_spin_unlock(&dbg_slave_lock);
/* Wait till all the CPUs have quit from the debugger. */
while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
cpu_relax();
}
kgdb_restore:
if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
int sstep_cpu = atomic_read(&kgdb_cpu_doing_single_step);
if (kgdb_info[sstep_cpu].task)
kgdb_sstep_pid = kgdb_info[sstep_cpu].task->pid;
else
kgdb_sstep_pid = 0;
}
if (arch_kgdb_ops.correct_hw_break)
arch_kgdb_ops.correct_hw_break();
if (trace_on)
tracing_on();
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
kgdb_info[cpu].exception_state &=
~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
kgdb_info[cpu].enter_kgdb--;
smp_mb__before_atomic_dec();
atomic_dec(&masters_in_kgdb);
/* Free kgdb_active */
atomic_set(&kgdb_active, -1);
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
raw_spin_unlock(&dbg_master_lock);
dbg_touch_watchdogs();
local_irq_restore(flags);
return kgdb_info[cpu].ret_state;
}
/*
* kgdb_handle_exception() - main entry point from a kernel exception
*
* Locking hierarchy:
* interface locks, if any (begin_session)
* kgdb lock (kgdb_active)
*/
int
kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
{
struct kgdb_state kgdb_var;
struct kgdb_state *ks = &kgdb_var;
ks->cpu = raw_smp_processor_id();
ks->ex_vector = evector;
ks->signo = signo;
ks->err_code = ecode;
ks->kgdb_usethreadid = 0;
ks->linux_regs = regs;
if (kgdb_reenter_check(ks))
return 0; /* Ouch, double exception ! */
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
if (kgdb_info[ks->cpu].enter_kgdb != 0)
return 0;
return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
}
int kgdb_nmicallback(int cpu, void *regs)
{
#ifdef CONFIG_SMP
struct kgdb_state kgdb_var;
struct kgdb_state *ks = &kgdb_var;
memset(ks, 0, sizeof(struct kgdb_state));
ks->cpu = cpu;
ks->linux_regs = regs;
debug_core: refactor locking for master/slave cpus For quite some time there have been problems with memory barriers and various races with NMI on multi processor systems using the kernel debugger. The algorithm for entering the kernel debug core and resuming kernel execution was racy and had several known edge case problems with attempting to debug something on a heavily loaded system using breakpoints that are hit repeatedly and quickly. The prior "locking" design entry worked as follows: * The atomic counter kgdb_active was used with atomic exchange in order to elect a master cpu out of all the cpus that may have taken a debug exception. * The master cpu increments all elements of passive_cpu_wait[]. * The master cpu issues the round up cpus message. * Each "slave cpu" that enters the debug core increments its own element in cpu_in_kgdb[]. * Each "slave cpu" spins on passive_cpu_wait[] until it becomes 0. * The master cpu debugs the system. The new scheme removes the two arrays of atomic counters and replaces them with 2 single counters. One counter is used to count the number of cpus waiting to become a master cpu (because one or more hit an exception). The second counter is use to indicate how many cpus have entered as slave cpus. The new entry logic works as follows: * One or more cpus enters via kgdb_handle_exception() and increments the masters_in_kgdb. Each cpu attempts to get the spin lock called dbg_master_lock. * The master cpu sets kgdb_active to the current cpu. * The master cpu takes the spinlock dbg_slave_lock. * The master cpu asks to round up all the other cpus. * Each slave cpu that is not already in kgdb_handle_exception() will enter and increment slaves_in_kgdb. Each slave will now spin try_locking on dbg_slave_lock. * The master cpu waits for the sum of masters_in_kgdb and slaves_in_kgdb to be equal to the sum of the online cpus. * The master cpu debugs the system. In the new design the kgdb_active can only be changed while holding dbg_master_lock. Stress testing has not turned up any further entry/exit races that existed in the prior locking design. The prior locking design suffered from atomic variables not being truly atomic (in the capacity as used by kgdb) along with memory barrier races. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Acked-by: Dongdong Deng <dongdong.deng@windriver.com>
2010-05-21 13:46:00 +00:00
if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
raw_spin_is_locked(&dbg_master_lock)) {
kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
return 0;
}
#endif
return 1;
}
static void kgdb_console_write(struct console *co, const char *s,
unsigned count)
{
unsigned long flags;
/* If we're debugging, or KGDB has not connected, don't try
* and print. */
if (!kgdb_connected || atomic_read(&kgdb_active) != -1 || dbg_kdb_mode)
return;
local_irq_save(flags);
gdbstub_msg_write(s, count);
local_irq_restore(flags);
}
static struct console kgdbcons = {
.name = "kgdb",
.write = kgdb_console_write,
.flags = CON_PRINTBUFFER | CON_ENABLED,
.index = -1,
};
#ifdef CONFIG_MAGIC_SYSRQ
static void sysrq_handle_dbg(int key)
{
if (!dbg_io_ops) {
printk(KERN_CRIT "ERROR: No KGDB I/O module available\n");
return;
}
if (!kgdb_connected) {
#ifdef CONFIG_KGDB_KDB
if (!dbg_kdb_mode)
printk(KERN_CRIT "KGDB or $3#33 for KDB\n");
#else
printk(KERN_CRIT "Entering KGDB\n");
#endif
}
kgdb_breakpoint();
}
static struct sysrq_key_op sysrq_dbg_op = {
.handler = sysrq_handle_dbg,
.help_msg = "debug(G)",
.action_msg = "DEBUG",
};
#endif
static int kgdb_panic_event(struct notifier_block *self,
unsigned long val,
void *data)
{
if (dbg_kdb_mode)
kdb_printf("PANIC: %s\n", (char *)data);
kgdb_breakpoint();
return NOTIFY_DONE;
}
static struct notifier_block kgdb_panic_event_nb = {
.notifier_call = kgdb_panic_event,
.priority = INT_MAX,
};
void __weak kgdb_arch_late(void)
{
}
void __init dbg_late_init(void)
{
dbg_is_early = false;
if (kgdb_io_module_registered)
kgdb_arch_late();
kdb_init(KDB_INIT_FULL);
}
static void kgdb_register_callbacks(void)
{
if (!kgdb_io_module_registered) {
kgdb_io_module_registered = 1;
kgdb_arch_init();
if (!dbg_is_early)
kgdb_arch_late();
atomic_notifier_chain_register(&panic_notifier_list,
&kgdb_panic_event_nb);
#ifdef CONFIG_MAGIC_SYSRQ
register_sysrq_key('g', &sysrq_dbg_op);
#endif
if (kgdb_use_con && !kgdb_con_registered) {
register_console(&kgdbcons);
kgdb_con_registered = 1;
}
}
}
static void kgdb_unregister_callbacks(void)
{
/*
* When this routine is called KGDB should unregister from the
* panic handler and clean up, making sure it is not handling any
* break exceptions at the time.
*/
if (kgdb_io_module_registered) {
kgdb_io_module_registered = 0;
atomic_notifier_chain_unregister(&panic_notifier_list,
&kgdb_panic_event_nb);
kgdb_arch_exit();
#ifdef CONFIG_MAGIC_SYSRQ
unregister_sysrq_key('g', &sysrq_dbg_op);
#endif
if (kgdb_con_registered) {
unregister_console(&kgdbcons);
kgdb_con_registered = 0;
}
}
}
/*
* There are times a tasklet needs to be used vs a compiled in
* break point so as to cause an exception outside a kgdb I/O module,
* such as is the case with kgdboe, where calling a breakpoint in the
* I/O driver itself would be fatal.
*/
static void kgdb_tasklet_bpt(unsigned long ing)
{
kgdb_breakpoint();
atomic_set(&kgdb_break_tasklet_var, 0);
}
static DECLARE_TASKLET(kgdb_tasklet_breakpoint, kgdb_tasklet_bpt, 0);
void kgdb_schedule_breakpoint(void)
{
if (atomic_read(&kgdb_break_tasklet_var) ||
atomic_read(&kgdb_active) != -1 ||
atomic_read(&kgdb_setting_breakpoint))
return;
atomic_inc(&kgdb_break_tasklet_var);
tasklet_schedule(&kgdb_tasklet_breakpoint);
}
EXPORT_SYMBOL_GPL(kgdb_schedule_breakpoint);
static void kgdb_initial_breakpoint(void)
{
kgdb_break_asap = 0;
printk(KERN_CRIT "kgdb: Waiting for connection from remote gdb...\n");
kgdb_breakpoint();
}
/**
* kgdb_register_io_module - register KGDB IO module
* @new_dbg_io_ops: the io ops vector
*
* Register it with the KGDB core.
*/
int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
{
int err;
spin_lock(&kgdb_registration_lock);
if (dbg_io_ops) {
spin_unlock(&kgdb_registration_lock);
printk(KERN_ERR "kgdb: Another I/O driver is already "
"registered with KGDB.\n");
return -EBUSY;
}
if (new_dbg_io_ops->init) {
err = new_dbg_io_ops->init();
if (err) {
spin_unlock(&kgdb_registration_lock);
return err;
}
}
dbg_io_ops = new_dbg_io_ops;
spin_unlock(&kgdb_registration_lock);
printk(KERN_INFO "kgdb: Registered I/O driver %s.\n",
new_dbg_io_ops->name);
/* Arm KGDB now. */
kgdb_register_callbacks();
if (kgdb_break_asap)
kgdb_initial_breakpoint();
return 0;
}
EXPORT_SYMBOL_GPL(kgdb_register_io_module);
/**
* kkgdb_unregister_io_module - unregister KGDB IO module
* @old_dbg_io_ops: the io ops vector
*
* Unregister it with the KGDB core.
*/
void kgdb_unregister_io_module(struct kgdb_io *old_dbg_io_ops)
{
BUG_ON(kgdb_connected);
/*
* KGDB is no longer able to communicate out, so
* unregister our callbacks and reset state.
*/
kgdb_unregister_callbacks();
spin_lock(&kgdb_registration_lock);
WARN_ON_ONCE(dbg_io_ops != old_dbg_io_ops);
dbg_io_ops = NULL;
spin_unlock(&kgdb_registration_lock);
printk(KERN_INFO
"kgdb: Unregistered I/O driver %s, debugger disabled.\n",
old_dbg_io_ops->name);
}
EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
int dbg_io_get_char(void)
{
int ret = dbg_io_ops->read_char();
if (ret == NO_POLL_CHAR)
return -1;
if (!dbg_kdb_mode)
return ret;
if (ret == 127)
return 8;
return ret;
}
/**
* kgdb_breakpoint - generate breakpoint exception
*
* This function will generate a breakpoint exception. It is used at the
* beginning of a program to sync up with a debugger and can be used
* otherwise as a quick means to stop program execution and "break" into
* the debugger.
*/
void kgdb_breakpoint(void)
{
atomic_inc(&kgdb_setting_breakpoint);
wmb(); /* Sync point before breakpoint */
arch_kgdb_breakpoint();
wmb(); /* Sync point after breakpoint */
atomic_dec(&kgdb_setting_breakpoint);
}
EXPORT_SYMBOL_GPL(kgdb_breakpoint);
static int __init opt_kgdb_wait(char *str)
{
kgdb_break_asap = 1;
kdb_init(KDB_INIT_EARLY);
if (kgdb_io_module_registered)
kgdb_initial_breakpoint();
return 0;
}
early_param("kgdbwait", opt_kgdb_wait);