[PATCH] blkcg: have bh disable for 32bit UP system reading 64bit stats

[PATCH] blkcg: have bh disable for 32bit UP system reading 64bit stats

[Hong Zhiguo]

From: Hong Zhiguo <zhiguohong-1Nz4purKYjRBDgjK7y7TUQ@public.gmane.org>

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.

Signed-off-by: Hong Zhiguo <zhiguohong-1Nz4purKYjRBDgjK7y7TUQ@public.gmane.org>
---
 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 ae6969a..2e34c38 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -430,9 +430,9 @@ 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;
 }
@@ -498,9 +498,9 @@ 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;
 }
-- 
1.8.1.2

Re: [PATCH] blkcg: have bh disable for 32bit UP system reading 64bit stats

[Tejun Heo]

On Wed, Nov 06, 2013 at 07:14:44PM +0800, Hong Zhiguo wrote:
> From: Hong Zhiguo <zhiguohong@tencent.com>
> 
> 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.
> 
> Signed-off-by: Hong Zhiguo <zhiguohong@tencent.com>

Acked-by: Tejun Heo <tj@kernel.org>

Jens, can you please pick this one up?  This probably needs to be
tagged for stable too.

Thanks!

-- 
tejun

Re: [PATCH] blkcg: have bh disable for 32bit UP system reading 64bit stats

[Jens Axboe]

On 11/20/2013 10:24 AM, Tejun Heo wrote:
> On Wed, Nov 06, 2013 at 07:14:44PM +0800, Hong Zhiguo wrote:
>> From: Hong Zhiguo <zhiguohong@tencent.com>
>>
>> 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.
>>
>> Signed-off-by: Hong Zhiguo <zhiguohong@tencent.com>
> 
> Acked-by: Tejun Heo <tj@kernel.org>
> 
> Jens, can you please pick this one up?  This probably needs to be
> tagged for stable too.

Yeah will do, thanks.

-- 
Jens Axboe