[PULL,13/27] blockdev: mirror: avoid potential deadlock when using iothread

Commit Message

Kevin Wolf Oct. 31, 2023, 6:59 p.m. UTC

From: Fiona Ebner <[e-mail]>

The bdrv_getlength() function is a generated co-wrapper and uses
AIO_WAIT_WHILE() to wait for the spawned coroutine. AIO_WAIT_WHILE()
expects the lock to be acquired exactly once.

Fix a case where it may be acquired twice. This can happen when the
source node is explicitly specified as the @replaces parameter or if the
source node is a filter node.

Signed-off-by: Fiona Ebner <[e-mail]>
Message-ID: <[e-mail]>
Reviewed-by: Kevin Wolf <[e-mail]>
Signed-off-by: Kevin Wolf <[e-mail]>
---
 blockdev.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

Patch

diff --git a/blockdev.c b/blockdev.c
index a01c62596b..877e3a26d4 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2968,6 +2968,7 @@  static void blockdev_mirror_common(const char *job_id, BlockDriverState *bs,
 
     if (replaces) {
         BlockDriverState *to_replace_bs;
+        AioContext *aio_context;
         AioContext *replace_aio_context;
         int64_t bs_size, replace_size;
 
@@ -2982,10 +2983,19 @@  static void blockdev_mirror_common(const char *job_id, BlockDriverState *bs,
             return;
         }
 
+        aio_context = bdrv_get_aio_context(bs);
         replace_aio_context = bdrv_get_aio_context(to_replace_bs);
-        aio_context_acquire(replace_aio_context);
+        /*
+         * bdrv_getlength() is a co-wrapper and uses AIO_WAIT_WHILE. Be sure not
+         * to acquire the same AioContext twice.
+         */
+        if (replace_aio_context != aio_context) {
+            aio_context_acquire(replace_aio_context);
+        }
         replace_size = bdrv_getlength(to_replace_bs);
-        aio_context_release(replace_aio_context);
+        if (replace_aio_context != aio_context) {
+            aio_context_release(replace_aio_context);
+        }
 
         if (replace_size < 0) {
             error_setg_errno(errp, -replace_size,