On Wed, 2009-01-14 at 18:18 +0100, Nick Piggin wrote: > > @@ -173,21 +237,21 @@ __mutex_lock_common(struct mutex *lock, > > 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(); > > Why does this need to do a preempt-disabled schedule? After we schedule > away, the next task can do arbitrary things or reschedule itself, so if > we have not anticipated such a condition here, then I can't see what > __schedule protects. At least a comment is in order? From: http://programming.kicks-ass.net/kernel-patches/mutex-adaptive-spin/mutex-preempt.patch Subject: mutex: preemption fixes From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Date: Wed Jan 14 15:36:26 CET 2009 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 explicitly disabling preemption and providing a schedule() variant that assumes preemption is already disabled. Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > Pity to add the call overhead to schedule just for this case. Good point, seeing any way around that? > BTW. __schedule shouldn't need to be asmlinkage? TBH I've no clue, probably not, Ingo? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
