linux/lib/kernel_lock.c

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/*
* lib/kernel_lock.c
*
* This is the traditional BKL - big kernel lock. Largely
* relegated to obsolescense, but used by various less
* important (or lazy) subsystems.
*/
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
#ifdef CONFIG_PREEMPT_BKL
/*
* The 'big kernel semaphore'
*
* This mutex is taken and released recursively by lock_kernel()
* and unlock_kernel(). It is transparently dropped and reaquired
* over schedule(). It is used to protect legacy code that hasn't
* been migrated to a proper locking design yet.
*
* Note: code locked by this semaphore will only be serialized against
* other code using the same locking facility. The code guarantees that
* the task remains on the same CPU.
*
* Don't use in new code.
*/
static DECLARE_MUTEX(kernel_sem);
/*
* Re-acquire the kernel semaphore.
*
* This function is called with preemption off.
*
* We are executing in schedule() so the code must be extremely careful
* about recursion, both due to the down() and due to the enabling of
* preemption. schedule() will re-check the preemption flag after
* reacquiring the semaphore.
*/
int __lockfunc __reacquire_kernel_lock(void)
{
struct task_struct *task = current;
int saved_lock_depth = task->lock_depth;
BUG_ON(saved_lock_depth < 0);
task->lock_depth = -1;
preempt_enable_no_resched();
down(&kernel_sem);
preempt_disable();
task->lock_depth = saved_lock_depth;
return 0;
}
void __lockfunc __release_kernel_lock(void)
{
up(&kernel_sem);
}
/*
* Getting the big kernel semaphore.
*/
void __lockfunc lock_kernel(void)
{
struct task_struct *task = current;
int depth = task->lock_depth + 1;
if (likely(!depth))
/*
* No recursion worries - we set up lock_depth _after_
*/
down(&kernel_sem);
task->lock_depth = depth;
}
void __lockfunc unlock_kernel(void)
{
struct task_struct *task = current;
BUG_ON(task->lock_depth < 0);
if (likely(--task->lock_depth < 0))
up(&kernel_sem);
}
#else
/*
* The 'big kernel lock'
*
* This spinlock is taken and released recursively by lock_kernel()
* and unlock_kernel(). It is transparently dropped and reaquired
* over schedule(). It is used to protect legacy code that hasn't
* been migrated to a proper locking design yet.
*
* Don't use in new code.
*/
static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kernel_flag);
/*
* Acquire/release the underlying lock from the scheduler.
*
* This is called with preemption disabled, and should
* return an error value if it cannot get the lock and
* TIF_NEED_RESCHED gets set.
*
* If it successfully gets the lock, it should increment
* the preemption count like any spinlock does.
*
* (This works on UP too - _raw_spin_trylock will never
* return false in that case)
*/
int __lockfunc __reacquire_kernel_lock(void)
{
while (!_raw_spin_trylock(&kernel_flag)) {
if (test_thread_flag(TIF_NEED_RESCHED))
return -EAGAIN;
cpu_relax();
}
preempt_disable();
return 0;
}
void __lockfunc __release_kernel_lock(void)
{
_raw_spin_unlock(&kernel_flag);
preempt_enable_no_resched();
}
/*
* These are the BKL spinlocks - we try to be polite about preemption.
* If SMP is not on (ie UP preemption), this all goes away because the
* _raw_spin_trylock() will always succeed.
*/
#ifdef CONFIG_PREEMPT
static inline void __lock_kernel(void)
{
preempt_disable();
if (unlikely(!_raw_spin_trylock(&kernel_flag))) {
/*
* If preemption was disabled even before this
* was called, there's nothing we can be polite
* about - just spin.
*/
if (preempt_count() > 1) {
_raw_spin_lock(&kernel_flag);
return;
}
/*
* Otherwise, let's wait for the kernel lock
* with preemption enabled..
*/
do {
preempt_enable();
while (spin_is_locked(&kernel_flag))
cpu_relax();
preempt_disable();
} while (!_raw_spin_trylock(&kernel_flag));
}
}
#else
/*
* Non-preemption case - just get the spinlock
*/
static inline void __lock_kernel(void)
{
_raw_spin_lock(&kernel_flag);
}
#endif
static inline void __unlock_kernel(void)
{
[PATCH] spinlock consolidation This patch (written by me and also containing many suggestions of Arjan van de Ven) does a major cleanup of the spinlock code. It does the following things: - consolidates and enhances the spinlock/rwlock debugging code - simplifies the asm/spinlock.h files - encapsulates the raw spinlock type and moves generic spinlock features (such as ->break_lock) into the generic code. - cleans up the spinlock code hierarchy to get rid of the spaghetti. Most notably there's now only a single variant of the debugging code, located in lib/spinlock_debug.c. (previously we had one SMP debugging variant per architecture, plus a separate generic one for UP builds) Also, i've enhanced the rwlock debugging facility, it will now track write-owners. There is new spinlock-owner/CPU-tracking on SMP builds too. All locks have lockup detection now, which will work for both soft and hard spin/rwlock lockups. The arch-level include files now only contain the minimally necessary subset of the spinlock code - all the rest that can be generalized now lives in the generic headers: include/asm-i386/spinlock_types.h | 16 include/asm-x86_64/spinlock_types.h | 16 I have also split up the various spinlock variants into separate files, making it easier to see which does what. The new layout is: SMP | UP ----------------------------|----------------------------------- asm/spinlock_types_smp.h | linux/spinlock_types_up.h linux/spinlock_types.h | linux/spinlock_types.h asm/spinlock_smp.h | linux/spinlock_up.h linux/spinlock_api_smp.h | linux/spinlock_api_up.h linux/spinlock.h | linux/spinlock.h /* * here's the role of the various spinlock/rwlock related include files: * * on SMP builds: * * asm/spinlock_types.h: contains the raw_spinlock_t/raw_rwlock_t and the * initializers * * linux/spinlock_types.h: * defines the generic type and initializers * * asm/spinlock.h: contains the __raw_spin_*()/etc. lowlevel * implementations, mostly inline assembly code * * (also included on UP-debug builds:) * * linux/spinlock_api_smp.h: * contains the prototypes for the _spin_*() APIs. * * linux/spinlock.h: builds the final spin_*() APIs. * * on UP builds: * * linux/spinlock_type_up.h: * contains the generic, simplified UP spinlock type. * (which is an empty structure on non-debug builds) * * linux/spinlock_types.h: * defines the generic type and initializers * * linux/spinlock_up.h: * contains the __raw_spin_*()/etc. version of UP * builds. (which are NOPs on non-debug, non-preempt * builds) * * (included on UP-non-debug builds:) * * linux/spinlock_api_up.h: * builds the _spin_*() APIs. * * linux/spinlock.h: builds the final spin_*() APIs. */ All SMP and UP architectures are converted by this patch. arm, i386, ia64, ppc, ppc64, s390/s390x, x64 was build-tested via crosscompilers. m32r, mips, sh, sparc, have not been tested yet, but should be mostly fine. From: Grant Grundler <grundler@parisc-linux.org> Booted and lightly tested on a500-44 (64-bit, SMP kernel, dual CPU). Builds 32-bit SMP kernel (not booted or tested). I did not try to build non-SMP kernels. That should be trivial to fix up later if necessary. I converted bit ops atomic_hash lock to raw_spinlock_t. Doing so avoids some ugly nesting of linux/*.h and asm/*.h files. Those particular locks are well tested and contained entirely inside arch specific code. I do NOT expect any new issues to arise with them. If someone does ever need to use debug/metrics with them, then they will need to unravel this hairball between spinlocks, atomic ops, and bit ops that exist only because parisc has exactly one atomic instruction: LDCW (load and clear word). From: "Luck, Tony" <tony.luck@intel.com> ia64 fix Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Arjan van de Ven <arjanv@infradead.org> Signed-off-by: Grant Grundler <grundler@parisc-linux.org> Cc: Matthew Wilcox <willy@debian.org> Signed-off-by: Hirokazu Takata <takata@linux-m32r.org> Signed-off-by: Mikael Pettersson <mikpe@csd.uu.se> Signed-off-by: Benoit Boissinot <benoit.boissinot@ens-lyon.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-10 07:25:56 +00:00
spin_unlock(&kernel_flag);
}
/*
* Getting the big kernel lock.
*
* This cannot happen asynchronously, so we only need to
* worry about other CPU's.
*/
void __lockfunc lock_kernel(void)
{
int depth = current->lock_depth+1;
if (likely(!depth))
__lock_kernel();
current->lock_depth = depth;
}
void __lockfunc unlock_kernel(void)
{
BUG_ON(current->lock_depth < 0);
if (likely(--current->lock_depth < 0))
__unlock_kernel();
}
#endif
EXPORT_SYMBOL(lock_kernel);
EXPORT_SYMBOL(unlock_kernel);