[PATCH 3.5 028/103] Update of blkg_stat and blkg_rwstat may happen in bh context. While u64_stats_fetch_retry is only preempt_disable on 32bit UP system. This is not enough to avoid preemption by bh and may read strange 64 bit value.

[Luis Henriques]

3.5.7.28 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hong Zhiguo <zhiguohong at tencent.com>

commit 2c575026fae6e63771bd2a4c1d407214a8096a89 upstream.

Signed-off-by: Hong Zhiguo <zhiguohong at tencent.com>
Acked-by: Tejun Heo <tj at kernel.org>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 block/blk-cgroup.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 8ac457c..b8521f4 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -261,9 +261,9 @@ static inline uint64_t blkg_stat_read(struct blkg_stat *stat)
 	uint64_t v;
 
 	do {
-		start = u64_stats_fetch_begin(&stat->syncp);
+		start = u64_stats_fetch_begin_bh(&stat->syncp);
 		v = stat->cnt;
-	} while (u64_stats_fetch_retry(&stat->syncp, start));
+	} while (u64_stats_fetch_retry_bh(&stat->syncp, start));
 
 	return v;
 }
@@ -317,9 +317,9 @@ static inline struct blkg_rwstat blkg_rwstat_read(struct blkg_rwstat *rwstat)
 	struct blkg_rwstat tmp;
 
 	do {
-		start = u64_stats_fetch_begin(&rwstat->syncp);
+		start = u64_stats_fetch_begin_bh(&rwstat->syncp);
 		tmp = *rwstat;
-	} while (u64_stats_fetch_retry(&rwstat->syncp, start));
+	} while (u64_stats_fetch_retry_bh(&rwstat->syncp, start));
 
 	return tmp;
 }
-- 
1.8.3.2