Re: [Qemu-devel] [PATCH] migration/rdma: unegister fd handler

["Dr. David Alan Gilbert" <dgilbert@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