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/copy-on-read.c b/block/copy-on-read.c
index 13ed4150a6..8cad979e29 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -121,9 +121,9 @@ static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
 }
 
 
-static int64_t cor_getlength(BlockDriverState *bs)
+static int64_t coroutine_fn cor_co_getlength(BlockDriverState *bs)
 {
-    return bdrv_getlength(bs->file->bs);
+    return bdrv_co_getlength(bs->file->bs);
 }
 
 
@@ -250,7 +250,7 @@ static BlockDriver bdrv_copy_on_read = {
     .bdrv_close                         = cor_close,
     .bdrv_child_perm                    = cor_child_perm,
 
-    .bdrv_getlength                     = cor_getlength,
+    .bdrv_co_getlength                  = cor_co_getlength,
 
     .bdrv_co_preadv_part                = cor_co_preadv_part,
     .bdrv_co_pwritev_part               = cor_co_pwritev_part,