[PATCH v2 2/8] block: protect write threshold QMP commands from concurrent requests

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

For simplicity, use bdrv_drained_begin/end to avoid concurrent
writes to the write threshold, or reading it while it is being set.
qmp_block_set_write_threshold is protected by the BQL.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/write-threshold.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/block/write-threshold.c b/block/write-threshold.c
index 63040fa4f2..77c74bdaa7 100644
--- a/block/write-threshold.c
+++ b/block/write-threshold.c
@@ -111,7 +111,6 @@ void qmp_block_set_write_threshold(const char *node_name,
                                    Error **errp)
 {
     BlockDriverState *bs;
-    AioContext *aio_context;
 
     bs = bdrv_find_node(node_name);
     if (!bs) {
@@ -119,10 +118,8 @@ void qmp_block_set_write_threshold(const char *node_name,
         return;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
-    aio_context_acquire(aio_context);
-
+    /* Avoid a concurrent write_threshold_disable.  */
+    bdrv_drained_begin(bs);
     bdrv_write_threshold_set(bs, threshold_bytes);
-
-    aio_context_release(aio_context);
+    bdrv_drained_end(bs);
 }
-- 
2.30.2