[PATCH 1/6] block: don't acquire AioContext lock in bdrv_drain_all()

[Stefan Hajnoczi]

There is no need for the AioContext lock in bdrv_drain_all() because
nothing in AIO_WAIT_WHILE() needs the lock and the condition is atomic.

Note that the NULL AioContext argument to AIO_WAIT_WHILE() is odd. In
the future it can be removed. There is an assertion in
AIO_WAIT_WHILE() that checks that we're in the main loop AioContext and
we would lose that check by dropping the argument. However, that was a
precursor to the GLOBAL_STATE_CODE()/IO_CODE() macros and is now a
duplicate check. So I think we won't lose much by dropping it, but let's
do a few more AIO_WAIT_WHILE_UNLOCKED() coversions of this sort to
confirm this is the case.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/block-backend.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 278b04ce69..d2b6b3652d 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1835,14 +1835,8 @@ void blk_drain_all(void)
     bdrv_drain_all_begin();
 
     while ((blk = blk_all_next(blk)) != NULL) {
-        AioContext *ctx = blk_get_aio_context(blk);
-
-        aio_context_acquire(ctx);
-
         /* We may have -ENOMEDIUM completions in flight */
-        AIO_WAIT_WHILE(ctx, qatomic_mb_read(&blk->in_flight) > 0);
-
-        aio_context_release(ctx);
+        AIO_WAIT_WHILE_UNLOCKED(NULL, qatomic_mb_read(&blk->in_flight) > 0);
     }
 
     bdrv_drain_all_end();
-- 
2.39.2