[PATCH] blk-cgroup: fix wrong unlock order when parse per blkg config

[PATCH] blk-cgroup: fix wrong unlock order when parse per blkg config

[Joseph Qi]

From: Joseph Qi <qijiang.qj-gPhfCIXyaqCqndwCJWfcng@public.gmane.org>

In case of error blkg in blkg_conf_prep, we should unlock
queue->queue_lock first and then rcu, just like blkg_conf_finish.

Signed-off-by: Joseph Qi <qijiang.qj-gPhfCIXyaqCqndwCJWfcng@public.gmane.org>
Signed-off-by: Joseph Qi <jiangqi903-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 block/blk-cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index bbe7ee0..cc017b2 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -823,8 +823,8 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 
 	if (IS_ERR(blkg)) {
 		ret = PTR_ERR(blkg);
-		rcu_read_unlock();
 		spin_unlock_irq(disk->queue->queue_lock);
+		rcu_read_unlock();
 		owner = disk->fops->owner;
 		put_disk(disk);
 		module_put(owner);
-- 
1.9.4

Re: [PATCH] blk-cgroup: fix wrong unlock order when parse per blkg config

[Tejun Heo]

Hello,

On Mon, Apr 24, 2017 at 06:52:05PM +0800, Joseph Qi wrote:
> From: Joseph Qi <qijiang.qj-gPhfCIXyaqCqndwCJWfcng@public.gmane.org>
> 
> In case of error blkg in blkg_conf_prep, we should unlock
> queue->queue_lock first and then rcu, just like blkg_conf_finish.

I get that this is inconsistent but why is this wrong?  If this is for
consistency, can you please explain so in the commit so that people
don't confuse it for an actual bug fix?

Thanks.

-- 
tejun

Re: [PATCH] blk-cgroup: fix wrong unlock order when parse per blkg config

[Joseph Qi]

Fine, I will explain so and resend it later.

Thanks,
Joseph

On 17/4/29 05:22, Tejun Heo wrote:
> Hello,
> 
> On Mon, Apr 24, 2017 at 06:52:05PM +0800, Joseph Qi wrote:
>> From: Joseph Qi <qijiang.qj-gPhfCIXyaqCqndwCJWfcng@public.gmane.org>
>>
>> In case of error blkg in blkg_conf_prep, we should unlock
>> queue->queue_lock first and then rcu, just like blkg_conf_finish.
> 
> I get that this is inconsistent but why is this wrong?  If this is for
> consistency, can you please explain so in the commit so that people
> don't confuse it for an actual bug fix?
> 
> Thanks.
> 

Re: [PATCH] blk-cgroup: fix wrong unlock order when parse per blkg config

[Joseph Qi]

Hi Tejun,
	
I've checked the upstream mainline and found that this is already fixed
as part of your commit 457e490f2b74 ("blkcg: allocate struct blkcg_gq
outside request queue spinlock"). So I do not have to resend it any
more, thanks.

Thanks,
Joseph

On 17/5/2 08:41, Joseph Qi wrote:
> Fine, I will explain so and resend it later.
> 
> Thanks,
> Joseph
> 
> On 17/4/29 05:22, Tejun Heo wrote:
>> Hello,
>>
>> On Mon, Apr 24, 2017 at 06:52:05PM +0800, Joseph Qi wrote:
>>> From: Joseph Qi <qijiang.qj-gPhfCIXyaqCqndwCJWfcng@public.gmane.org>
>>>
>>> In case of error blkg in blkg_conf_prep, we should unlock
>>> queue->queue_lock first and then rcu, just like blkg_conf_finish.
>>
>> I get that this is inconsistent but why is this wrong?  If this is for
>> consistency, can you please explain so in the commit so that people
>> don't confuse it for an actual bug fix?
>>
>> Thanks.
>>