block: Fix locking in external_snapshot_prepare()

bdrv_img_create() polls internally (when calling bdrv_create(), which is a co_wrapper), so it can't be called while holding the lock of any AioContext except the current one without causing deadlocks. Drop the lock around the call in external_snapshot_prepare(). Signed-off-by: Kevin Wolf <[email protected]> Message-Id: <[email protected]> Reviewed-by: Emanuele Giuseppe Esposito <[email protected]> Signed-off-by: Kevin Wolf <[email protected]>
xuyb1999 · Dec 15, 2022 · e135505 · e135505
1 parent 617f3a9
commit e135505
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diff --git a/block.c b/block.c
@@ -6924,6 +6924,10 @@ bool bdrv_op_blocker_is_empty(BlockDriverState *bs)
     return true;
 }
 
+/*
+ * Must not be called while holding the lock of an AioContext other than the
+ * current one.
+ */
 void bdrv_img_create(const char *filename, const char *fmt,
                      const char *base_filename, const char *base_fmt,
                      char *options, uint64_t img_size, int flags, bool quiet,

diff --git a/blockdev.c b/blockdev.c
@@ -1507,10 +1507,14 @@ static void external_snapshot_prepare(BlkActionState *common,
                 goto out;
             }
             bdrv_refresh_filename(state->old_bs);
+
+            aio_context_release(aio_context);
             bdrv_img_create(new_image_file, format,
                             state->old_bs->filename,
                             state->old_bs->drv->format_name,
                             NULL, size, flags, false, &local_err);
+            aio_context_acquire(aio_context);
+
             if (local_err) {
                 error_propagate(errp, local_err);
                 goto out;