Gitweb:     http://git.kernel.org/linus/41719b03091911028116155deddc5eedf8c45e37
Commit:     41719b03091911028116155deddc5eedf8c45e37
Parent:     93d81d1aca26e64a75d06a85f7e128b5f49053e7
Author:     Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Wed Jan 14 15:36:26 2009 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed Jan 14 18:09:00 2009 +0100

    mutex: preemption fixes
    
    The problem is that dropping the spinlock right before schedule is a voluntary
    preemption point and can cause a schedule, right after which we schedule again.
    
    Fix this inefficiency by keeping preemption disabled until we schedule, do this
    by explicity disabling preemption and providing a schedule() variant that
    assumes preemption is already disabled.
    
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 include/linux/sched.h |    1 +
 kernel/mutex.c        |    5 ++++-
 kernel/sched.c        |   10 +++++++---
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4cae9b8..9f0b372 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -328,6 +328,7 @@ extern signed long schedule_timeout(signed long timeout);
 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);
 asmlinkage void schedule(void);
 
 struct nsproxy;
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 357c6d2..524ffc3 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -131,6 +131,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	struct mutex_waiter waiter;
 	unsigned long flags;
 
+	preempt_disable();
 	spin_lock_mutex(&lock->wait_lock, flags);
 
 	debug_mutex_lock_common(lock, &waiter);
@@ -170,13 +171,14 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 			spin_unlock_mutex(&lock->wait_lock, flags);
 
 			debug_mutex_free_waiter(&waiter);
+			preempt_enable();
 			return -EINTR;
 		}
 		__set_task_state(task, state);
 
 		/* didnt get the lock, go to sleep: */
 		spin_unlock_mutex(&lock->wait_lock, flags);
-		schedule();
+		__schedule();
 		spin_lock_mutex(&lock->wait_lock, flags);
 	}
 
@@ -193,6 +195,7 @@ done:
 	spin_unlock_mutex(&lock->wait_lock, flags);
 
 	debug_mutex_free_waiter(&waiter);
+	preempt_enable();
 
 	return 0;
 }
diff --git a/kernel/sched.c b/kernel/sched.c
index 8be2c13..b001c13 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4538,15 +4538,13 @@ pick_next_task(struct rq *rq, struct task_struct *prev)
 /*
  * schedule() is the main scheduler function.
  */
-asmlinkage void __sched schedule(void)
+asmlinkage void __sched __schedule(void)
 {
 	struct task_struct *prev, *next;
 	unsigned long *switch_count;
 	struct rq *rq;
 	int cpu;
 
-need_resched:
-	preempt_disable();
 	cpu = smp_processor_id();
 	rq = cpu_rq(cpu);
 	rcu_qsctr_inc(cpu);
@@ -4603,7 +4601,13 @@ need_resched_nonpreemptible:
 
 	if (unlikely(reacquire_kernel_lock(current) < 0))
 		goto need_resched_nonpreemptible;
+}
 
+asmlinkage void __sched schedule(void)
+{
+need_resched:
+	preempt_disable();
+	__schedule();
 	preempt_enable_no_resched();
 	if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
 		goto need_resched;
--
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