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Re: [Qemu-block] [Qemu-devel] [PATCH 1/9] blockdev: hold AioContext for
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From: |
Stefan Hajnoczi |
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Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH 1/9] blockdev: hold AioContext for bdrv_unref() in external_snapshot_clean() |
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Date: |
Wed, 6 Dec 2017 11:31:55 +0000 |
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User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Tue, Dec 05, 2017 at 08:36:32AM -0600, Eric Blake wrote:
> On 12/05/2017 04:41 AM, Stefan Hajnoczi wrote:
> > bdrv_unref() requires the AioContext lock because bdrv_flush() uses
> > BDRV_POLL_WHILE(), which assumes the AioContext is currently held. If
> > BDRV_POLL_WHILE() runs without AioContext held the
> > pthread_mutex_unlock() call in aio_context_release() fails.
> >
> > This patch moves bdrv_unref() into the AioContext locked region to solve
> > the following pthread_mutex_unlock() failure:
> >
> > #0 0x00007f566181969b in raise () at /lib64/libc.so.6
> > #1 0x00007f566181b3b1 in abort () at /lib64/libc.so.6
> > #2 0x00005592cd590458 in error_exit (err=<optimized out>, address@hidden
> > <__func__.23977> "qemu_mutex_unlock") at util/qemu-thread-posix.c:36
> > #3 0x00005592cd96e738 in qemu_mutex_unlock (address@hidden) at
> > util/qemu-thread-posix.c:96
> > #4 0x00005592cd969b69 in aio_context_release (address@hidden) at
> > util/async.c:507
> > #5 0x00005592cd8ead78 in bdrv_flush (address@hidden) at block/io.c:2478
> > #6 0x00005592cd89df30 in bdrv_close (bs=0x5592cfa87210) at block.c:3207
> > #7 0x00005592cd89df30 in bdrv_delete (bs=0x5592cfa87210) at block.c:3395
> > #8 0x00005592cd89df30 in bdrv_unref (bs=0x5592cfa87210) at block.c:4418
> > #9 0x00005592cd6b7f86 in qmp_transaction (dev_list=<optimized out>,
> > has_props=<optimized out>, props=<optimized out>, address@hidden) at
> > blockdev.c:2308
> >
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > ---
> > blockdev.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Reviewed-by: Eric Blake <address@hidden>
>
> I know the series is too big/late for 2.11, but is this one patch worth
> having?
This fix is not critical for 2.11. The bug shouldn't be triggered under
normal circumstances.
The bug was exposed while developing qemu-iotests 202, which uses
unconventional commands (blockdev-add to create BDSes with no -drive or
BlockBackend).
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- [Qemu-block] [PATCH 0/9] blockdev: fix QMP 'transaction' with IOThreads, Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 1/9] blockdev: hold AioContext for bdrv_unref() in external_snapshot_clean(), Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 2/9] block: don't keep AioContext acquired after external_snapshot_prepare(), Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 3/9] block: don't keep AioContext acquired after drive_backup_prepare(), Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 4/9] block: don't keep AioContext acquired after blockdev_backup_prepare(), Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 5/9] block: don't keep AioContext acquired after internal_snapshot_prepare(), Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 6/9] block: drop unused BlockDirtyBitmapState->aio_context field, Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 7/9] iothread: add iothread_by_id() API, Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 8/9] blockdev: add x-blockdev-set-iothread testing command, Stefan Hajnoczi, 2017/12/05
- [Qemu-block] [PATCH 9/9] qemu-iotests: add 202 external snapshots IOThread test, Stefan Hajnoczi, 2017/12/05