Re: [PULL v2 0/6] Migration 20240917 patches

[Peter Xu <peterx@redhat.com>]

On Thu, Sep 19, 2024 at 12:29:43PM -0400, Peter Xu wrote:
> > > CID 1527402: In migrate_fd_cleanup() Coverity thinks there's
> > > a race because we read s->to_dst_file in the "if (s->to_dst_file)"
> > > check without holding the qemu_file_lock. This might be a
> > > false-positive because the race Coverity identifies happens
> > > if two threads both call migrate_fd_cleanup() at the same
> > > time, which is probably not permitted. (But OTOH taking a
> > > mutex gets you for free any necessary memory barriers...)
> > 
> > Yes, we shouldn't rely on mental gymnastics to prove that there's no
> > concurrent access.
> > 
> > @peterx, that RH bug you showed me could very well be caused by this
> > race, except that I don't see how fd_cleanup could race with
> > itself. Just having the lock would probably save us time even thinking
> > about it.
> 
> I can send a patch for this one.

Oh btw I think that may not be the same issue.. I did observe one memory
order issue only happens on aarch64 when looking at that bug, and I _feel_
like there can be more.

Bandan (after his long PTO) from our team will keep looking.  Since that
can relatively constantly reproduce (IIRC..), we do have chance to figure
it out, sooner or later.

-- 
Peter Xu