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mutex: Use p->on_cpu for the adaptive spin

Since we now have p->on_cpu unconditionally available, use it to
re-implement mutex_spin_on_owner.

Requested-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110405152728.826338173@chello.nl
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1 parent 3ca7a44 commit c6eb3dda25892f1f974f5420f63e6721aab02f6f Peter Zijlstra committed with Ingo Molnar Apr 5, 2011
Showing with 39 additions and 56 deletions.
  1. +1 −1 include/linux/mutex.h
  2. +1 −1 include/linux/sched.h
  3. +1 −1 kernel/mutex-debug.c
  4. +1 −1 kernel/mutex-debug.h
  5. +1 −1 kernel/mutex.c
  6. +1 −1 kernel/mutex.h
  7. +33 −50 kernel/sched.c
View
2 include/linux/mutex.h
@@ -51,7 +51,7 @@ struct mutex {
spinlock_t wait_lock;
struct list_head wait_list;
#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
- struct thread_info *owner;
+ struct task_struct *owner;
#endif
#ifdef CONFIG_DEBUG_MUTEXES
const char *name;
View
2 include/linux/sched.h
@@ -360,7 +360,7 @@ extern signed long schedule_timeout_interruptible(signed long timeout);
extern signed long schedule_timeout_killable(signed long timeout);
extern signed long schedule_timeout_uninterruptible(signed long timeout);
asmlinkage void schedule(void);
-extern int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner);
+extern int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner);
struct nsproxy;
struct user_namespace;
View
2 kernel/mutex-debug.c
@@ -75,7 +75,7 @@ void debug_mutex_unlock(struct mutex *lock)
return;
DEBUG_LOCKS_WARN_ON(lock->magic != lock);
- DEBUG_LOCKS_WARN_ON(lock->owner != current_thread_info());
+ DEBUG_LOCKS_WARN_ON(lock->owner != current);
DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
mutex_clear_owner(lock);
}
View
2 kernel/mutex-debug.h
@@ -29,7 +29,7 @@ extern void debug_mutex_init(struct mutex *lock, const char *name,
static inline void mutex_set_owner(struct mutex *lock)
{
- lock->owner = current_thread_info();
+ lock->owner = current;
}
static inline void mutex_clear_owner(struct mutex *lock)
View
2 kernel/mutex.c
@@ -160,7 +160,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
*/
for (;;) {
- struct thread_info *owner;
+ struct task_struct *owner;
/*
* If we own the BKL, then don't spin. The owner of
View
2 kernel/mutex.h
@@ -19,7 +19,7 @@
#ifdef CONFIG_SMP
static inline void mutex_set_owner(struct mutex *lock)
{
- lock->owner = current_thread_info();
+ lock->owner = current;
}
static inline void mutex_clear_owner(struct mutex *lock)
View
83 kernel/sched.c
@@ -4173,70 +4173,53 @@ asmlinkage void __sched schedule(void)
EXPORT_SYMBOL(schedule);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
-/*
- * Look out! "owner" is an entirely speculative pointer
- * access and not reliable.
- */
-int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
-{
- unsigned int cpu;
- struct rq *rq;
- if (!sched_feat(OWNER_SPIN))
- return 0;
+static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
+{
+ bool ret = false;
-#ifdef CONFIG_DEBUG_PAGEALLOC
- /*
- * Need to access the cpu field knowing that
- * DEBUG_PAGEALLOC could have unmapped it if
- * the mutex owner just released it and exited.
- */
- if (probe_kernel_address(&owner->cpu, cpu))
- return 0;
-#else
- cpu = owner->cpu;
-#endif
+ rcu_read_lock();
+ if (lock->owner != owner)
+ goto fail;
/*
- * Even if the access succeeded (likely case),
- * the cpu field may no longer be valid.
+ * Ensure we emit the owner->on_cpu, dereference _after_ checking
+ * lock->owner still matches owner, if that fails, owner might
+ * point to free()d memory, if it still matches, the rcu_read_lock()
+ * ensures the memory stays valid.
*/
- if (cpu >= nr_cpumask_bits)
- return 0;
+ barrier();
- /*
- * We need to validate that we can do a
- * get_cpu() and that we have the percpu area.
- */
- if (!cpu_online(cpu))
- return 0;
+ ret = owner->on_cpu;
+fail:
+ rcu_read_unlock();
- rq = cpu_rq(cpu);
+ return ret;
+}
- for (;;) {
- /*
- * Owner changed, break to re-assess state.
- */
- if (lock->owner != owner) {
- /*
- * If the lock has switched to a different owner,
- * we likely have heavy contention. Return 0 to quit
- * optimistic spinning and not contend further:
- */
- if (lock->owner)
- return 0;
- break;
- }
+/*
+ * Look out! "owner" is an entirely speculative pointer
+ * access and not reliable.
+ */
+int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
+{
+ if (!sched_feat(OWNER_SPIN))
+ return 0;
- /*
- * Is that owner really running on that cpu?
- */
- if (task_thread_info(rq->curr) != owner || need_resched())
+ while (owner_running(lock, owner)) {
+ if (need_resched())
return 0;
arch_mutex_cpu_relax();
}
+ /*
+ * If the owner changed to another task there is likely
+ * heavy contention, stop spinning.
+ */
+ if (lock->owner)
+ return 0;
+
return 1;
}
#endif

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