[v2,1/9] blockdev: hold AioContext for bdrv_unref() in external_snapshot_clean()

Message ID 20171206144550.22295-2-stefanha@redhat.com
State New
Headers show
Series
  • blockdev: fix QMP 'transaction' with IOThreads
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Commit Message

Stefan Hajnoczi Dec. 6, 2017, 2:45 p.m.
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>, msg=msg@entry=0x5592cdaf6d60 <__func__.23977> "qemu_mutex_unlock") at util/qemu-thread-posix.c:36
  #3  0x00005592cd96e738 in qemu_mutex_unlock (mutex=mutex@entry=0x5592ce9505e0) at util/qemu-thread-posix.c:96
  #4  0x00005592cd969b69 in aio_context_release (ctx=ctx@entry=0x5592ce950580) at util/async.c:507
  #5  0x00005592cd8ead78 in bdrv_flush (bs=bs@entry=0x5592cfa87210) 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>, errp=errp@entry=0x7ffe4a1fc9d8) at blockdev.c:2308

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 blockdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Eric Blake Dec. 7, 2017, 8:32 p.m. | #1
On 12/06/2017 08:45 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:
> 

> diff --git a/blockdev.c b/blockdev.c
> index 56a6b24a0b..3c8d994ced 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1812,8 +1812,8 @@ static void external_snapshot_clean(BlkActionState *common)
>                               DO_UPCAST(ExternalSnapshotState, common, common);
>      if (state->aio_context) {
>          bdrv_drained_end(state->old_bs);
> -        aio_context_release(state->aio_context);
>          bdrv_unref(state->new_bs);
> +        aio_context_release(state->aio_context);

Reviewed-by: Eric Blake <eblake@redhat.com>

Patch

diff --git a/blockdev.c b/blockdev.c
index 56a6b24a0b..3c8d994ced 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1812,8 +1812,8 @@  static void external_snapshot_clean(BlkActionState *common)
                              DO_UPCAST(ExternalSnapshotState, common, common);
     if (state->aio_context) {
         bdrv_drained_end(state->old_bs);
-        aio_context_release(state->aio_context);
         bdrv_unref(state->new_bs);
+        aio_context_release(state->aio_context);
     }
 }