Logically below race could trigger with the old code:
test program migration thread
------------ ----------------
wait_until('postcopy-pause')
postcopy_pause()
set_state('postcopy-pause')
do_postcopy_recover()
arm s->to_dst_file with new fd
release s->to_dst_file [1]
Here [1] could have released the just-installed recoverying channel. Then the
migration could hang without really resuming.
Instead, it should be very safe to release the fd before setting the state into
'postcopy-pause', because there's no reason for any other thread to touch it
during 'postcopy-active'.
Dave reported a very rare postcopy recovery hang that the migration-test
program waited for the migration to complete in migrate_postcopy_complete().
We do suspect it's the same thing that we're gonna fix here. Hard to tell.
However since we've noticed this, fix this irrelevant of the hang report.
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201021212721.440373-6-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
d246ea5039