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Date: Wed, 23 Jan 2019 09:31:37 +0000
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Message-ID: <20190123093137.GA2193@work-vm>
References: <20190122173111.29821-1-dgilbert@redhat.com>
	<20190123081351.GB18231@xz-x1>
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Subject: Re: [Qemu-devel] [PATCH] migration/rdma: unegister fd handler
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To: Peter Xu <peterx@redhat.com>
Cc: qemu-devel@nongnu.org, jemmy858585@gmail.com, quintela@redhat.com

* Peter Xu (peterx@redhat.com) wrote:
> On Tue, Jan 22, 2019 at 05:31:11PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > Unregister the fd handler before we destroy the channel,
> > otherwise we've got a race where we might land in the
> > fd handler just as we're closing the device.
> > 
> > (The race is quite data dependent, you just have to have
> > the right set of devices for it to trigger).
> > 
> > Corresponds to RH bz: https://bugzilla.redhat.com/show_bug.cgi?id=1666601
> > 
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> (Could the crash happened because the same fd number is re-used after
>  the RDMA channel was destroyed?  Then when the fd has an event, it'll
>  be delivered to rdma_cm_poll_handler() while the fd is not really the
>  RDMA channel handle any more)

That's an interesting thought, I'd assumed it was just a race, but being
dependent on the fd numbering would explain why it was so delicate to
reproduce it.

> Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks!

Dave

> Regards,
> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK