[PATCH 3.8 60/91] 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.

[Kamal Mostafa]

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

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

From: Hong Zhiguo <zhiguoh...@tencent.com>

commit 2c575026fae6e63771bd2a4c1d407214a8096a89 upstream.

Signed-off-by: Hong Zhiguo <zhiguoh...@tencent.com>
Acked-by: Tejun Heo <t...@kernel.org>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Kamal Mostafa <ka...@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 2459730..6f33c3f 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -370,9 +370,9 @@ 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;
 }
@@ -426,9 +426,9 @@ 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

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