linux-kernel - Re: [PATCH] fs/afs/flock and fs/locks: Fix possible sleep-in-atomic bugs in posix_lock

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Date:   Sat, 07 Oct 2017 06:36:57 -0400
From:   Jeff Layton <jlayton@...hat.com>
To:     Jia-Ju Bai <baijiaju1990@....com>, dhowells@...hat.com,
        viro@...iv.linux.org.uk, bfields@...ldses.org
Cc:     linux-fsdevel@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/afs/flock and fs/locks: Fix possible sleep-in-atomic
 bugs in posix_lock_file

On Sat, 2017-10-07 at 17:55 +0800, Jia-Ju Bai wrote:
> The kernel may sleep under a spinlock, and the function call paths are:
> afs_do_unlk (acquire the spinlock)
>   posix_lock_file
>     posix_lock_inode (fs/locks.c)
>       locks_get_lock_context
>         kmem_cache_alloc(GFP_KERNEL) --> may sleep
> 
> afs_do_setlk (acquire the spinlock)
>   posix_lock_file
>     posix_lock_inode (fs/locks.c)
>       locks_get_lock_context
>         kmem_cache_alloc(GFP_KERNEL) --> may sleep
> 
> To fix them, GFP_KERNEL is replaced with GFP_ATOMIC.
> These bugs are found by my static analysis tool and my code review.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
> ---
>  fs/locks.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 1bd71c4..975cc62 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -222,7 +222,7 @@ struct file_lock_list_struct {
>  	if (likely(ctx) || type == F_UNLCK)
>  		goto out;
>  
> -	ctx = kmem_cache_alloc(flctx_cache, GFP_KERNEL);
> +	ctx = kmem_cache_alloc(flctx_cache, GFP_ATOMIC);
>  	if (!ctx)
>  		goto out;
>  

NAK

This needs to be fixed in the AFS code. It should not be calling these
functions with a spinlock held.

-- 
Jeff Layton <jlayton@...hat.com>