block: access io_limits_disabled with atomic ops

Reviewed-by: Stefan Hajnoczi <[email protected]> Reviewed-by: Alberto Garcia <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]> Message-Id: <[email protected]> Signed-off-by: Fam Zheng <[email protected]>
cfriedt · Jun 15, 2017 · d993b85 · d993b85
1 parent 414c2ec
commit d993b85
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Showing 3 changed files with 5 additions and 4 deletions.
diff --git a/block/block-backend.c b/block/block-backend.c
@@ -1953,7 +1953,7 @@ static void blk_root_drained_begin(BdrvChild *child)
     /* Note that blk->root may not be accessible here yet if we are just
      * attaching to a BlockDriverState that is drained. Use child instead. */
 
-    if (blk->public.io_limits_disabled++ == 0) {
+    if (atomic_fetch_inc(&blk->public.io_limits_disabled) == 0) {
         throttle_group_restart_blk(blk);
     }
 }
@@ -1964,7 +1964,7 @@ static void blk_root_drained_end(BdrvChild *child)
     assert(blk->quiesce_counter);
 
     assert(blk->public.io_limits_disabled);
-    --blk->public.io_limits_disabled;
+    atomic_dec(&blk->public.io_limits_disabled);
 
     if (--blk->quiesce_counter == 0) {
         if (blk->dev_ops && blk->dev_ops->drained_end) {

diff --git a/block/throttle-groups.c b/block/throttle-groups.c
@@ -240,7 +240,7 @@ static bool throttle_group_schedule_timer(BlockBackend *blk, bool is_write)
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
     bool must_wait;
 
-    if (blkp->io_limits_disabled) {
+    if (atomic_read(&blkp->io_limits_disabled)) {
         return false;
     }
 

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
@@ -80,7 +80,8 @@ typedef struct BlockBackendPublic {
     CoQueue      throttled_reqs[2];
 
     /* Nonzero if the I/O limits are currently being ignored; generally
-     * it is zero.  */
+     * it is zero.  Accessed with atomic operations.
+     */
     unsigned int io_limits_disabled;
 
     /* The following fields are protected by the ThrottleGroup lock.