block: access io_plugged with atomic ops

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20170605123908.18777-7-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>

diff --git a/block/io.c b/block/io.c
index 4a598299a92184a5071289b5a6f0196ca7c01c97..bb1c9c5432bfd5a24eb0d269f5df4eff744a0fef 100644 (file)
--- a/block/io.c
+++ b/block/io.c
@@ -2645,7 +2645,7 @@ void bdrv_io_plug(BlockDriverState *bs)
         bdrv_io_plug(child->bs);
     }
 
-    if (bs->io_plugged++ == 0) {
+    if (atomic_fetch_inc(&bs->io_plugged) == 0) {
         BlockDriver *drv = bs->drv;
         if (drv && drv->bdrv_io_plug) {
             drv->bdrv_io_plug(bs);
@@ -2658,7 +2658,7 @@ void bdrv_io_unplug(BlockDriverState *bs)
     BdrvChild *child;
 
     assert(bs->io_plugged);
-    if (--bs->io_plugged == 0) {
+    if (atomic_fetch_dec(&bs->io_plugged) == 1) {
         BlockDriver *drv = bs->drv;
         if (drv && drv->bdrv_io_unplug) {
             drv->bdrv_io_unplug(bs);

diff --git a/include/block/block_int.h b/include/block/block_int.h
index cf544b7f3106ddf4c9633aa657812f4be6ea8cc9..091b5d361c9e873273a75383fa292bb4513fc436 100644 (file)
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -611,9 +611,6 @@ struct BlockDriverState {
     uint64_t write_threshold_offset;
     NotifierWithReturn write_threshold_notifier;
 
-    /* counter for nested bdrv_io_plug */
-    unsigned io_plugged;
-
     QLIST_HEAD(, BdrvTrackedRequest) tracked_requests;
     CoQueue flush_queue;                  /* Serializing flush queue */
     bool active_flush_req;                /* Flush request in flight? */
@@ -639,6 +636,11 @@ struct BlockDriverState {
      */
     bool wakeup;
 
+    /* counter for nested bdrv_io_plug.
+     * Accessed with atomic ops.
+    */
+    unsigned io_plugged;
+
     /* do we need to tell the quest if we have a volatile write cache? */
     int enable_write_cache;