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Re: [libvirt] [PATCH] unlock eventLoop before calling callback function



On Mon, Mar 07, 2011 at 11:15:38 +0000, Daniel P. Berrange wrote:
> > -        if (eventLoop.handles[i].ff)
> > +        if (eventLoop.handles[i].ff) {
> > +            virMutexUnlock(&eventLoop.lock);
> >              (eventLoop.handles[i].ff)(eventLoop.handles[i].opaque);
> > +            virMutexLock(&eventLoop.lock);
> > +        }
>
> I'm a little concerned as to whether the rest of the code in
> virEventCleanupHandles/CleanupTimeouts is safe, if we release
> the lock here. eg, if some other thread calls virEventAddTimeout
> of AddHandle, is there any way this could cause problems for us
> here. So far I think this is safe because AddTimeout/AddHandle
> will simply append to the end of the array we're iterating over,
> but would like a second opinion before ACK'ing

I don't think it's safe to unlock eventloop.lock even in the existing
Dispatch{Timeouts,Handles} cases because Add{Timeout,Handle} use realloc which
is allowed to allocate a new array, move the contents of the old one into it
and free the old array. So the for loop can easily end up accessing memory
which has already been freed.

Jirka


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