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, 4 insertions, 1 deletions

diff --git a/include/block/block_int-io.h b/include/block/block_int-io.h
index 37b0fd9..4430bf4 100644
--- a/include/block/block_int-io.h
+++ b/include/block/block_int-io.h
@@ -122,7 +122,10 @@ int coroutine_fn bdrv_co_copy_range_to(BdrvChild *src, int64_t src_offset,
                                        BdrvRequestFlags read_flags,
                                        BdrvRequestFlags write_flags);
 
-int bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint);
+int coroutine_fn bdrv_co_refresh_total_sectors(BlockDriverState *bs,
+                                               int64_t hint);
+int co_wrapper_mixed
+bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint);
 
 BdrvChild *bdrv_cow_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_child(BlockDriverState *bs);