Re: [Xen-devel] [PATCH 00/12] libxl: fork: SIGCHLD flexibility

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Jackson writes ("Re: [Xen-devel] [PATCH 00/12] libxl: fork: SIGCHLD 
flexibility"):
> I have just looked at the code in vireventpoll.c and there is nothing
> that stops this being a problem.

While looking at this I found:

        /* Add 20ms fuzz so we don't pointlessly spin doing
         * <10ms sleeps, particularly on kernels with low HZ
         * it is fine that a timer expires 20ms earlier than
         * requested
         */
        if (eventLoop.timeouts[i].expiresAt <= (now+20)) {

This is Not Good.  Result is that maybe libvirt wakes up, calls the
timeout callback function for libxl, libxl compares the time with the
timeout requested and thinks "oh this must be some previous callback
with the same struct" (due to essential workaround for inherent API
race) and does nothing.
                                                            
Ian.

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