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
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 94b48bd..c75471db 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -51,7 +51,7 @@
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;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3435837..1738504 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -360,7 +360,7 @@
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;
diff --git a/kernel/mutex-debug.c b/kernel/mutex-debug.c
index ec815a9..73da83a 100644
--- a/kernel/mutex-debug.c
+++ b/kernel/mutex-debug.c
@@ -75,7 +75,7 @@
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);
}
diff --git a/kernel/mutex-debug.h b/kernel/mutex-debug.h
index 57d527a..0799fd3 100644
--- a/kernel/mutex-debug.h
+++ b/kernel/mutex-debug.h
@@ -29,7 +29,7 @@
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)
diff --git a/kernel/mutex.c b/kernel/mutex.c
index c4195fa..fe4706c 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -160,7 +160,7 @@
*/
for (;;) {
- struct thread_info *owner;
+ struct task_struct *owner;
/*
* If we own the BKL, then don't spin. The owner of
diff --git a/kernel/mutex.h b/kernel/mutex.h
index 67578ca..4115fbf 100644
--- a/kernel/mutex.h
+++ b/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)
diff --git a/kernel/sched.c b/kernel/sched.c
index cd2593e..55cc503 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4173,70 +4173,53 @@
EXPORT_SYMBOL(schedule);
#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
+
+static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
+{
+ bool ret = false;
+
+ rcu_read_lock();
+ if (lock->owner != owner)
+ goto fail;
+
+ /*
+ * 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.
+ */
+ barrier();
+
+ ret = owner->on_cpu;
+fail:
+ rcu_read_unlock();
+
+ return ret;
+}
+
/*
* Look out! "owner" is an entirely speculative pointer
* access and not reliable.
*/
-int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
+int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
{
- unsigned int cpu;
- struct rq *rq;
-
if (!sched_feat(OWNER_SPIN))
return 0;
-#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
-
- /*
- * Even if the access succeeded (likely case),
- * the cpu field may no longer be valid.
- */
- if (cpu >= nr_cpumask_bits)
- return 0;
-
- /*
- * We need to validate that we can do a
- * get_cpu() and that we have the percpu area.
- */
- if (!cpu_online(cpu))
- return 0;
-
- rq = cpu_rq(cpu);
-
- 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;
- }
-
- /*
- * 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
