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, 4 deletions

diff --git a/block/quorum.c b/block/quorum.c
index 7f21c03f1f..d1dcf2eaba 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -754,19 +754,19 @@ static int coroutine_fn quorum_co_pwrite_zeroes(BlockDriverState *bs,
                              flags | BDRV_REQ_ZERO_WRITE);
 }
 
-static int64_t quorum_getlength(BlockDriverState *bs)
+static int64_t coroutine_fn quorum_co_getlength(BlockDriverState *bs)
 {
     BDRVQuorumState *s = bs->opaque;
     int64_t result;
     int i;
 
     /* check that all file have the same length */
-    result = bdrv_getlength(s->children[0]->bs);
+    result = bdrv_co_getlength(s->children[0]->bs);
     if (result < 0) {
         return result;
     }
     for (i = 1; i < s->num_children; i++) {
-        int64_t value = bdrv_getlength(s->children[i]->bs);
+        int64_t value = bdrv_co_getlength(s->children[i]->bs);
         if (value < 0) {
             return value;
         }
@@ -1283,7 +1283,7 @@ static BlockDriver bdrv_quorum = {
 
     .bdrv_co_flush                      = quorum_co_flush,
 
-    .bdrv_getlength                     = quorum_getlength,
+    .bdrv_co_getlength                  = quorum_co_getlength,
 
     .bdrv_co_preadv                     = quorum_co_preadv,
     .bdrv_co_pwritev                    = quorum_co_pwritev,