Messages in this thread | | | Date | Tue, 6 Dec 2005 17:23:53 -0800 | From | "Randy.Dunlap" <> | Subject | Re: robust futex heap support patch |
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On Tue, 6 Dec 2005 15:06:12 +0100 (MET) Esben Nielsen wrote:
> On Mon, 5 Dec 2005, david singleton wrote: > > > > > On Dec 5, 2005, at 2:30 PM, Esben Nielsen wrote: > > > > I'm currently trying to close a race condition between futex_wait_robust > > and futex_wake_robust that Dave Carlson is seeing on his SMP system. > > > > The scenario is as follows: > > > > Thread A locks an pthread_mutex via the fast path and does not enter > > the kernel. > > > > Thread B tries to lock the lock and sees it is already locked. Thread > > B sets the > > waiters flag in the lock and enters the kernel to lock the lock on > > behalf of > > thread A and then block on the mutex waiting for it's release. > > > > Thread A unlocks the lock and sees the waiters flag set. Thread A gets > > to the futex_wake_robust before Thread B can get to futex_wait_robust. > > > > Thread A sees that it does not own the lock in the kernel and was > > returning EINVAL. > > > > patch-2.6.14-rt21-rf8 was a preliminary patch for Dave Carlson to try > > and get more information about > > the race condition. ( rf8 and rf9 are still returning EAGAIN from > > thread B trying to > > do the futex_wait_robust and the library should be retrying with > > EAGAIN, but it currently isn't). > > > > *nod* > I just pointed out that you can't make thread A loop the way you do. > > What I would do was to do the user space flag checks while having the > raw spinlock of the rt_mutex. That way you are sure that stuff in the > kernel is serialized. But I don't know what to do exactly to do in > there.... > > > > When I get the race condition closed I'll post the patch and notify > > everyone on lkml > > and the robustmutexes mailing lists. > > Where can I sign up to that mailing list? I would like to follow the > development, although I don't have much time to contibute.
http://lists.osdl.org/mailman/listinfo/robustmutexes/
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