Messages in this thread | | | Subject | Re: [PATCH 2/3] ipc/sem.c: handle spurious wakeups | From | Peter Zijlstra <> | Date | Wed, 12 Oct 2011 09:09:35 +0200 |
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On Tue, 2011-10-11 at 14:54 -0700, Andrew Morton wrote: > On Sat, 24 Sep 2011 19:37:11 +0200 > Manfred Spraul <manfred@colorfullife.com> wrote: > > > semtimedop() does not handle spurious wakeups, it returns -EINTR to user space. > > Most other schedule() users would just loop and not return to user space. > > The patch adds such a loop to semtimedop() > > What is a "spurious wakeup" and how can a process receive one?
Its a wakeup unrelated to the condition its waiting for. They shouldn't happen (often) but all wait loops should deal with them. Sadly of course most out of core wait loops don't :-(
> I'm wondering about the userspace-visible effects of this change, and > any compatibility issues?
For this particular case it would be returning to userspace with -EINTR without a signal having been raised what so ever. Not a big deal as userspace it supposed to be able to deal with -EINTR and retry.
Also, these spurious wakeups hardly ever happen in the current kernel, I only noticed it because I made them slightly more likely with a patch currently on the back-burner until I figure out a sane way to audit all 1400+ schedule() and co. callsites.
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