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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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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;
}