This function, in addition to be called by a generated_co_wrapper, is also called by the blk_* API. The strategy is to always take the lock at the function called when the coroutine is created, to avoid recursive locking.
Protecting bdrv_co_flush() implies that the following BlockDriver callbacks always called with graph rdlock taken: - bdrv_co_flush - bdrv_co_flush_to_os - bdrv_co_flush_to_disk Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com> --- block/block-backend.c | 3 ++- block/io.c | 1 + include/block/block_int-common.h | 6 ++++++ 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/block/block-backend.c b/block/block-backend.c index 083ed6009e..d660772375 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1759,8 +1759,9 @@ int coroutine_fn blk_co_pdiscard(BlockBackend *blk, int64_t offset, /* To be called between exactly one pair of blk_inc/dec_in_flight() */ static int coroutine_fn blk_co_do_flush(BlockBackend *blk) { - blk_wait_while_drained(blk); IO_CODE(); + blk_wait_while_drained(blk); + GRAPH_RDLOCK_GUARD(); if (!blk_is_available(blk)) { return -ENOMEDIUM; diff --git a/block/io.c b/block/io.c index cfc201ef91..0bf3919939 100644 --- a/block/io.c +++ b/block/io.c @@ -2757,6 +2757,7 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs) int ret = 0; IO_CODE(); + assert_bdrv_graph_readable(); bdrv_inc_in_flight(bs); if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs) || diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h index 64c5bb64de..bab0521943 100644 --- a/include/block/block_int-common.h +++ b/include/block/block_int-common.h @@ -661,6 +661,8 @@ struct BlockDriver { * Flushes all data for all layers by calling bdrv_co_flush for underlying * layers, if needed. This function is needed for deterministic * synchronization of the flush finishing callback. + * + * Called with graph rdlock taken. */ int coroutine_fn (*bdrv_co_flush)(BlockDriverState *bs); @@ -671,6 +673,8 @@ struct BlockDriver { /* * Flushes all data that was already written to the OS all the way down to * the disk (for example file-posix.c calls fsync()). + * + * Called with graph rdlock taken. */ int coroutine_fn (*bdrv_co_flush_to_disk)(BlockDriverState *bs); @@ -678,6 +682,8 @@ struct BlockDriver { * Flushes all internal caches to the OS. The data may still sit in a * writeback cache of the host OS, but it will survive a crash of the qemu * process. + * + * Called with graph rdlock held. */ int coroutine_fn (*bdrv_co_flush_to_os)(BlockDriverState *bs); -- 2.31.1