block: Convert bdrv_refresh_total_sectors() to co_wrapper_mixed

BlockDriver->bdrv_getlength is categorized as IO callback, and it
currently doesn't run in a coroutine. We should let it take a graph
rdlock since the callback traverses the block nodes graph, which however
is only possible in a coroutine.

Therefore turn it into a co_wrapper to move the actual function into a
coroutine where the lock can be taken.

Because now this function creates a new coroutine and polls, we need to
take the AioContext lock where it is missing, for the only reason that
internally co_wrapper calls AIO_WAIT_WHILE and it expects to release the
AioContext lock.

This is especially messy when a co_wrapper creates a coroutine and polls
in bdrv_open_driver, because this function has so many callers in so
many context that it can easily lead to deadlocks. Therefore the new
rule for bdrv_open_driver is that the caller must always hold the
AioContext lock of the given bs (except if it is a coroutine), because
the function calls bdrv_refresh_total_sectors() which is now a
co_wrapper.

Once the rwlock is ultimated and placed in every place it needs to be,
we will poll using AIO_WAIT_WHILE_UNLOCKED and remove the AioContext
lock.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230113204212.359076-7-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/block/mirror.c b/block/mirror.c
index 634815d78d..7ed4dbde04 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -910,13 +910,13 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
         goto immediate_exit;
     }
 
-    s->bdev_length = bdrv_getlength(bs);
+    s->bdev_length = bdrv_co_getlength(bs);
     if (s->bdev_length < 0) {
         ret = s->bdev_length;
         goto immediate_exit;
     }
 
-    target_length = blk_getlength(s->target);
+    target_length = blk_co_getlength(s->target);
     if (target_length < 0) {
         ret = target_length;
         goto immediate_exit;