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



On Mon, Mar 07, 2011 at 14:13:23 +0100, Jiri Denemark wrote:
> 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.

Eh, my fingers were faster than my brain :-) Dispatch* are safe since they do
anything with the old pointer after getting back from a callback.

Jirka


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