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mutex: preemption fixes

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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>
This commit is contained in:
Peter Zijlstra 2009-01-14 15:36:26 +01:00 committed by Ingo Molnar
parent 93d81d1aca
commit 41719b0309
3 changed files with 12 additions and 4 deletions
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1
include/linux/sched.h
View file

@ -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;

5
kernel/mutex.c
View file

@ -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;
}

10
kernel/sched.c
View file

@ -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;