[PATCH] block/blk-cgroup-rwstat: use data_race() for online test

[Tao Cui]

From: Tao Cui <cuitao@xxxxxxxxxx>

blkg_rwstat_recursive_sum() reads pos_blkg->online without the queue
lock that its doc comment requires, since blkcg_print_blkgs() stopped
holding it in 56cc24f59c14.  Concurrent blkg_create/destroy flips
->online, tripping KCSAN.  The race is harmless (RCU-protected, stale
online only causes minor stat noise).  Use data_race() to annotate
the intentional lockless read.

Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>
---
 block/blk-cgroup-rwstat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-cgroup-rwstat.c b/block/blk-cgroup-rwstat.c
index aae910713814..71f74052ae03 100644
--- a/block/blk-cgroup-rwstat.c
+++ b/block/blk-cgroup-rwstat.c
@@ -107,7 +107,7 @@ void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
 	blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
 		struct blkg_rwstat *rwstat;
 
-		if (!pos_blkg->online)
+		if (!data_race(pos_blkg->online))
 			continue;
 
 		if (pol) {
-- 
2.43.0