05.02.2021 19:01, Kevin Wolf wrote:
Am 27.11.2020 um 15:45 hat Vladimir Sementsov-Ogievskiy geschrieben:
During reopen we may add backing bs from other aio context, which may
lead to changing original context of top bs.
We are going to move graph modification to prepare stage. So, it will
be possible that bdrv_flush() in bdrv_reopen_prepare called on bs in
non-original aio context, which we didn't aquire which leads to crash.
More correct would be to acquire all aio context we are going to work
with. And the simplest ways is to just acquire all of them. It may be
optimized later if needed.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
I'm afraid it's not as easy. Holding the lock of more than one
AioContext is always a bit risky with respect to deadlocks.
For example, changing the AioContext of a node with
bdrv_set_aio_context_ignore() has explicit rules that are now violated:
* The caller must own the AioContext lock for the old AioContext of bs, but it
* must not own the AioContext lock for new_context (unless new_context is the
* same as the current context of bs).
Draining while holding all AioContext locks is suspicious, too. I think
I have seen deadlocks before, which is why bdrv_drain_all_*() are
careful to only ever lock a single AioContext at a time.
Kevin
That's not good :\ Hmm, probably we just should flush everything before all
graph modifications.
--
Best regards,
Vladimir
