linux/kernel/power/process.c
Roland McGrath 13b1c3d4b4 freezer vs stopped or traced
This changes the "freezer" code used by suspend/hibernate in its treatment
of tasks in TASK_STOPPED (job control stop) and TASK_TRACED (ptrace) states.

As I understand it, the intent of the "freezer" is to hold all tasks
from doing anything significant.  For this purpose, TASK_STOPPED and
TASK_TRACED are "frozen enough".  It's possible the tasks might resume
from ptrace calls (if the tracer were unfrozen) or from signals
(including ones that could come via timer interrupts, etc).  But this
doesn't matter as long as they quickly block again while "freezing" is
in effect.  Some minor adjustments to the signal.c code make sure that
try_to_freeze() very shortly follows all wakeups from both kinds of
stop.  This lets the freezer code safely leave stopped tasks unmolested.

Changing this fixes the longstanding bug of seeing after resuming from
suspend/hibernate your shell report "[1] Stopped" and the like for all
your jobs stopped by ^Z et al, as if you had freshly fg'd and ^Z'd them.
It also removes from the freezer the arcane special case treatment for
ptrace'd tasks, which relied on intimate knowledge of ptrace internals.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-03-04 07:59:54 -08:00

280 lines
6.3 KiB
C

/*
* drivers/power/process.c - Functions for starting/stopping processes on
* suspend transitions.
*
* Originally from swsusp.
*/
#undef DEBUG
#include <linux/interrupt.h>
#include <linux/suspend.h>
#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
/*
* Timeout for stopping processes
*/
#define TIMEOUT (20 * HZ)
#define FREEZER_KERNEL_THREADS 0
#define FREEZER_USER_SPACE 1
static inline int freezeable(struct task_struct * p)
{
if ((p == current) ||
(p->flags & PF_NOFREEZE) ||
(p->exit_state != 0))
return 0;
return 1;
}
/*
* freezing is complete, mark current process as frozen
*/
static inline void frozen_process(void)
{
if (!unlikely(current->flags & PF_NOFREEZE)) {
current->flags |= PF_FROZEN;
wmb();
}
clear_freeze_flag(current);
}
/* Refrigerator is place where frozen processes are stored :-). */
void refrigerator(void)
{
/* Hmm, should we be allowed to suspend when there are realtime
processes around? */
long save;
task_lock(current);
if (freezing(current)) {
frozen_process();
task_unlock(current);
} else {
task_unlock(current);
return;
}
save = current->state;
pr_debug("%s entered refrigerator\n", current->comm);
spin_lock_irq(&current->sighand->siglock);
recalc_sigpending(); /* We sent fake signal, clean it up */
spin_unlock_irq(&current->sighand->siglock);
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!frozen(current))
break;
schedule();
}
pr_debug("%s left refrigerator\n", current->comm);
__set_current_state(save);
}
static void fake_signal_wake_up(struct task_struct *p)
{
unsigned long flags;
spin_lock_irqsave(&p->sighand->siglock, flags);
signal_wake_up(p, 0);
spin_unlock_irqrestore(&p->sighand->siglock, flags);
}
static int has_mm(struct task_struct *p)
{
return (p->mm && !(p->flags & PF_BORROWED_MM));
}
/**
* freeze_task - send a freeze request to given task
* @p: task to send the request to
* @with_mm_only: if set, the request will only be sent if the task has its
* own mm
* Return value: 0, if @with_mm_only is set and the task has no mm of its
* own or the task is frozen, 1, otherwise
*
* The freeze request is sent by seting the tasks's TIF_FREEZE flag and
* either sending a fake signal to it or waking it up, depending on whether
* or not it has its own mm (ie. it is a user land task). If @with_mm_only
* is set and the task has no mm of its own (ie. it is a kernel thread),
* its TIF_FREEZE flag should not be set.
*
* The task_lock() is necessary to prevent races with exit_mm() or
* use_mm()/unuse_mm() from occuring.
*/
static int freeze_task(struct task_struct *p, int with_mm_only)
{
int ret = 1;
task_lock(p);
if (freezing(p)) {
if (has_mm(p)) {
if (!signal_pending(p))
fake_signal_wake_up(p);
} else {
if (with_mm_only)
ret = 0;
else
wake_up_state(p, TASK_INTERRUPTIBLE);
}
} else {
rmb();
if (frozen(p)) {
ret = 0;
} else {
if (has_mm(p)) {
set_freeze_flag(p);
fake_signal_wake_up(p);
} else {
if (with_mm_only) {
ret = 0;
} else {
set_freeze_flag(p);
wake_up_state(p, TASK_INTERRUPTIBLE);
}
}
}
}
task_unlock(p);
return ret;
}
static void cancel_freezing(struct task_struct *p)
{
unsigned long flags;
if (freezing(p)) {
pr_debug(" clean up: %s\n", p->comm);
clear_freeze_flag(p);
spin_lock_irqsave(&p->sighand->siglock, flags);
recalc_sigpending_and_wake(p);
spin_unlock_irqrestore(&p->sighand->siglock, flags);
}
}
static int try_to_freeze_tasks(int freeze_user_space)
{
struct task_struct *g, *p;
unsigned long end_time;
unsigned int todo;
struct timeval start, end;
s64 elapsed_csecs64;
unsigned int elapsed_csecs;
do_gettimeofday(&start);
end_time = jiffies + TIMEOUT;
do {
todo = 0;
read_lock(&tasklist_lock);
do_each_thread(g, p) {
if (frozen(p) || !freezeable(p))
continue;
if (!freeze_task(p, freeze_user_space))
continue;
/*
* Now that we've done set_freeze_flag, don't
* perturb a task in TASK_STOPPED or TASK_TRACED.
* It is "frozen enough". If the task does wake
* up, it will immediately call try_to_freeze.
*/
if (!task_is_stopped_or_traced(p) &&
!freezer_should_skip(p))
todo++;
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
yield(); /* Yield is okay here */
if (time_after(jiffies, end_time))
break;
} while (todo);
do_gettimeofday(&end);
elapsed_csecs64 = timeval_to_ns(&end) - timeval_to_ns(&start);
do_div(elapsed_csecs64, NSEC_PER_SEC / 100);
elapsed_csecs = elapsed_csecs64;
if (todo) {
/* This does not unfreeze processes that are already frozen
* (we have slightly ugly calling convention in that respect,
* and caller must call thaw_processes() if something fails),
* but it cleans up leftover PF_FREEZE requests.
*/
printk("\n");
printk(KERN_ERR "Freezing of tasks failed after %d.%02d seconds "
"(%d tasks refusing to freeze):\n",
elapsed_csecs / 100, elapsed_csecs % 100, todo);
show_state();
read_lock(&tasklist_lock);
do_each_thread(g, p) {
task_lock(p);
if (freezing(p) && !freezer_should_skip(p))
printk(KERN_ERR " %s\n", p->comm);
cancel_freezing(p);
task_unlock(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
} else {
printk("(elapsed %d.%02d seconds) ", elapsed_csecs / 100,
elapsed_csecs % 100);
}
return todo ? -EBUSY : 0;
}
/**
* freeze_processes - tell processes to enter the refrigerator
*/
int freeze_processes(void)
{
int error;
printk("Freezing user space processes ... ");
error = try_to_freeze_tasks(FREEZER_USER_SPACE);
if (error)
goto Exit;
printk("done.\n");
printk("Freezing remaining freezable tasks ... ");
error = try_to_freeze_tasks(FREEZER_KERNEL_THREADS);
if (error)
goto Exit;
printk("done.");
Exit:
BUG_ON(in_atomic());
printk("\n");
return error;
}
static void thaw_tasks(int thaw_user_space)
{
struct task_struct *g, *p;
read_lock(&tasklist_lock);
do_each_thread(g, p) {
if (!freezeable(p))
continue;
if (!p->mm == thaw_user_space)
continue;
thaw_process(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
}
void thaw_processes(void)
{
printk("Restarting tasks ... ");
thaw_tasks(FREEZER_KERNEL_THREADS);
thaw_tasks(FREEZER_USER_SPACE);
schedule();
printk("done.\n");
}
EXPORT_SYMBOL(refrigerator);