[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
2013-12-10T08:12:06Z

From: Hong Zhiguo <zhiguohong@tencent.com>

commit 2c575026fae6e63771bd2a4c1d407214a8096a89 upstream.

Signed-off-by: Hong Zhiguo <zhiguohong@tencent.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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;
}