[PATCH 3.12 45/62] 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.

[Greg Kroah-Hartman]

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

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

From: Hong Zhiguo <zhiguohong@xxxxxxxxxxx>

commit 2c575026fae6e63771bd2a4c1d407214a8096a89 upstream.

Signed-off-by: Hong Zhiguo <zhiguohong@xxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 block/blk-cgroup.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -430,9 +430,9 @@ static inline uint64_t blkg_stat_read(st
 	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;
 }
@@ -498,9 +498,9 @@ static inline struct blkg_rwstat blkg_rw
 	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;
 }


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