linux-kernel - Re: [PATCH] fs: xfs: Fix a lock-twice and sleep-in-atomic bug in xfs

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Date:   Mon, 05 Jun 2017 16:56:20 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     Shan Hai <shan.hai@...cle.com>
CC:     darrick.wong@...cle.com, linux-xfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: xfs: Fix a lock-twice and sleep-in-atomic bug in
 xfs_iget

On 06/05/2017 04:32 PM, Shan Hai wrote:
>
>
> On 2017年06月05日 16:17, Jia-Ju Bai wrote:
>> The driver may sleep under a read rcu lock, and function call path is:
>> xfs_iget (acquire the lock by rcu_read_lock)
>>    "goto out_error_or_again" after xfs_iget_cache_hit
>>      delay
>>        schedule_timeout_uninterruptible --> may sleep
>> Meanwhile, the rcu_read_lock will be called twice in this situation.
>>
>> To fix it, the lock is released before "goto".
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
>> ---
>>   fs/xfs/xfs_icache.c |    4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
>> index f61c84f8..c2a4722 100644
>> --- a/fs/xfs/xfs_icache.c
>> +++ b/fs/xfs/xfs_icache.c
>> @@ -600,8 +600,10 @@ struct xfs_inode *
>>         if (ip) {
>>           error = xfs_iget_cache_hit(pag, ip, ino, flags, lock_flags);
>> -        if (error)
>> +        if (error) {
>> +            rcu_read_unlock();
>
> Seems you are going to double unlock by doing this, since it is 
> unlocked in the xfs_iget_cache_hit.
>
> Thanks
> Shan Hai
>
>>               goto out_error_or_again;
>> +        }
>>       } else {
>>           rcu_read_unlock();
>>           XFS_STATS_INC(mp, xs_ig_missed);
>
I think you are right. Please ignore my patch.

Thanks,
Jia-Ju Bai