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, 3 insertions, 3 deletions

diff --git a/block/blkreplay.c b/block/blkreplay.c
index e3b6a3efb2..16543f585a 100644
--- a/block/blkreplay.c
+++ b/block/blkreplay.c
@@ -40,9 +40,9 @@ fail:
     return ret;
 }
 
-static int64_t blkreplay_getlength(BlockDriverState *bs)
+static int64_t coroutine_fn blkreplay_co_getlength(BlockDriverState *bs)
 {
-    return bdrv_getlength(bs->file->bs);
+    return bdrv_co_getlength(bs->file->bs);
 }
 
 /* This bh is used for synchronization of return from coroutines.
@@ -136,7 +136,7 @@ static BlockDriver bdrv_blkreplay = {
 
     .bdrv_open              = blkreplay_open,
     .bdrv_child_perm        = bdrv_default_perms,
-    .bdrv_getlength         = blkreplay_getlength,
+    .bdrv_co_getlength      = blkreplay_co_getlength,
 
     .bdrv_co_preadv         = blkreplay_co_preadv,
     .bdrv_co_pwritev        = blkreplay_co_pwritev,