block: Add missing locking in bdrv_co_drain_bh_cb()

bdrv_do_drained_begin/end() assume that they are called with the
AioContext lock of bs held. If we call drain functions from a coroutine
with the AioContext lock held, we yield and schedule a BH to move out of
coroutine context. This means that the lock for the home context of the
coroutine is released and must be re-acquired in the bottom half.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index 6f8a487..9801e7f 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -90,6 +90,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co);
 void coroutine_fn qemu_coroutine_yield(void);
 
 /**
+ * Get the AioContext of the given coroutine
+ */
+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);
+
+/**
  * Get the currently executing coroutine
  */
 Coroutine *coroutine_fn qemu_coroutine_self(void);