Re: [PATCH 2/3] ipc/sem.c: handle spurious wakeups

[Manfred Spraul]

On 10/11/2011 11:54 PM, Andrew Morton wrote:
> On Sat, 24 Sep 2011 19:37:11 +0200
> Manfred Spraul<manfred@xxxxxxxxxxxxxxxx>  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?
A spurious wakeup means that someone calls wake_up_process() without a 
proper reason.
The most common case would be a wake_up_process() that was somehow delayed.

Peter's patch made such delayed wakeups very common, this is how we 
found the issue.

The "standard" kernel primitives handle such wakeups, ipc/sem.c doesn't 
handle that.

> I'm wondering about the userspace-visible effects of this change, and
> any compatibility issues?
This change has no userspace visible effects.

--
    Manfred
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