[PATCH 15/20] block-gen: assert that {bdrv/blk}_co_flush is always called with graph rdlock taken

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

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 <eesposit@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