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authorLinus Torvalds <torvalds@linux-foundation.org>2013-09-04 08:18:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-04 08:18:19 -0700
commit4689550bb278cb142979c313a0d608e802c6711b (patch)
treef8776c28f1328ab4077132c636c2706f12c793aa /kernel/mutex.c
parentb854e4de0bf88d094476af82c0d5a80f6f2af916 (diff)
parent15e71911fcc655508e02f767a3d9b8b138051d2b (diff)
Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull core/locking changes from Ingo Molnar: "Main changes: - another mutex optimization, from Davidlohr Bueso - improved lglock lockdep tracking, from Michel Lespinasse - [ assorted smaller updates, improvements, cleanups. ]" * 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: generic-ipi/locking: Fix misleading smp_call_function_any() description hung_task debugging: Print more info when reporting the problem mutex: Avoid label warning when !CONFIG_MUTEX_SPIN_ON_OWNER mutex: Do not unnecessarily deal with waiters mutex: Fix/document access-once assumption in mutex_can_spin_on_owner() lglock: Update lockdep annotations to report recursive local locks lockdep: Introduce lock_acquire_exclusive()/shared() helper macros
Diffstat (limited to 'kernel/mutex.c')
-rw-r--r--kernel/mutex.c43
1 files changed, 20 insertions, 23 deletions
diff --git a/kernel/mutex.c b/kernel/mutex.c
index a52ee7bb830d..6d647aedffea 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -209,11 +209,13 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
*/
static inline int mutex_can_spin_on_owner(struct mutex *lock)
{
+ struct task_struct *owner;
int retval = 1;
rcu_read_lock();
- if (lock->owner)
- retval = lock->owner->on_cpu;
+ owner = ACCESS_ONCE(lock->owner);
+ if (owner)
+ retval = owner->on_cpu;
rcu_read_unlock();
/*
* if lock->owner is not set, the mutex owner may have just acquired
@@ -461,7 +463,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* performed the optimistic spinning cannot be done.
*/
if (ACCESS_ONCE(ww->ctx))
- break;
+ goto slowpath;
}
/*
@@ -472,7 +474,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
owner = ACCESS_ONCE(lock->owner);
if (owner && !mutex_spin_on_owner(lock, owner)) {
mspin_unlock(MLOCK(lock), &node);
- break;
+ goto slowpath;
}
if ((atomic_read(&lock->count) == 1) &&
@@ -499,7 +501,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* the owner complete.
*/
if (!owner && (need_resched() || rt_task(task)))
- break;
+ goto slowpath;
/*
* The cpu_relax() call is a compiler barrier which forces
@@ -513,6 +515,10 @@ slowpath:
#endif
spin_lock_mutex(&lock->wait_lock, flags);
+ /* once more, can we acquire the lock? */
+ if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1))
+ goto skip_wait;
+
debug_mutex_lock_common(lock, &waiter);
debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
@@ -520,9 +526,6 @@ slowpath:
list_add_tail(&waiter.list, &lock->wait_list);
waiter.task = task;
- if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1))
- goto done;
-
lock_contended(&lock->dep_map, ip);
for (;;) {
@@ -536,7 +539,7 @@ slowpath:
* other waiters:
*/
if (MUTEX_SHOW_NO_WAITER(lock) &&
- (atomic_xchg(&lock->count, -1) == 1))
+ (atomic_xchg(&lock->count, -1) == 1))
break;
/*
@@ -561,24 +564,25 @@ slowpath:
schedule_preempt_disabled();
spin_lock_mutex(&lock->wait_lock, flags);
}
+ mutex_remove_waiter(lock, &waiter, current_thread_info());
+ /* set it to 0 if there are no waiters left: */
+ if (likely(list_empty(&lock->wait_list)))
+ atomic_set(&lock->count, 0);
+ debug_mutex_free_waiter(&waiter);
-done:
+skip_wait:
+ /* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
- /* got the lock - rejoice! */
- mutex_remove_waiter(lock, &waiter, current_thread_info());
mutex_set_owner(lock);
if (!__builtin_constant_p(ww_ctx == NULL)) {
- struct ww_mutex *ww = container_of(lock,
- struct ww_mutex,
- base);
+ struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
struct mutex_waiter *cur;
/*
* This branch gets optimized out for the common case,
* and is only important for ww_mutex_lock.
*/
-
ww_mutex_lock_acquired(ww, ww_ctx);
ww->ctx = ww_ctx;
@@ -592,15 +596,8 @@ done:
}
}
- /* set it to 0 if there are no waiters left: */
- if (likely(list_empty(&lock->wait_list)))
- atomic_set(&lock->count, 0);
-
spin_unlock_mutex(&lock->wait_lock, flags);
-
- debug_mutex_free_waiter(&waiter);
preempt_enable();
-
return 0;
err: