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| H A D | block.c | diff a2aabf88958119ec7d3022287eff6bcc924c90a8 Wed Apr 28 10:17:57 CDT 2021 Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> block: bdrv_reopen_multiple(): move bdrv_flush to separate pre-prepare
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.
To avoid this problem move bdrv_flush() to be a separate reopen stage
before bdrv_reopen_prepare().
This doesn't seem correct to acquire only one aio context and not all
contexts participating in reopen. But it's not obvious how to do it
correctly, keeping in mind:
1. rules of bdrv_set_aio_context_ignore() that requires new_context
lock not being held
2. possible deadlocks because of holding all (or several?) AioContext
locks
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210428151804.439460-30-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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