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

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Date:   Mon, 5 Jun 2017 16:32:48 +0800
From:   Shan Hai <shan.hai@...cle.com>
To:     Jia-Ju Bai <baijiaju1990@....com>, darrick.wong@...cle.com
Cc:     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 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);