[PULL 11/27] blockjob: drop AioContext lock before calling bdrv_graph_wrlock()

[Kevin Wolf]

From: Fiona Ebner <f.ebner@proxmox.com>

Same rationale as in 31b2ddfea3 ("graph-lock: Unlock the AioContext
while polling"). Otherwise, a deadlock can happen.

The alternative would be to pass a BlockDriverState along to
bdrv_graph_wrlock(), but there is no BlockDriverState readily
available and it's also better conceptually, because the lock is held
for the job.

The function is always called with the job's AioContext lock held, via
one of the .abort, .clean, .free or .prepare job driver functions.
Thus, it's safe to drop it.

While mirror_exit_common() does hold a second AioContext lock while
calling block_job_remove_all_bdrv(), that is for the main thread's
AioContext and does not need to be dropped (bdrv_graph_wrlock(bs) also
skips dropping the lock if bdrv_get_aio_context(bs) ==
qemu_get_aio_context()).

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20231019131936.414246-2-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 blockjob.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/blockjob.c b/blockjob.c
index 807f992b59..953dc1b6dc 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -198,7 +198,9 @@ void block_job_remove_all_bdrv(BlockJob *job)
      * one to make sure that such a concurrent access does not attempt
      * to process an already freed BdrvChild.
      */
+    aio_context_release(job->job.aio_context);
     bdrv_graph_wrlock(NULL);
+    aio_context_acquire(job->job.aio_context);
     while (job->nodes) {
         GSList *l = job->nodes;
         BdrvChild *c = l->data;
-- 
2.41.0