linux-kernel - Re: [PATCH] kernfs: fix barrier usage in __kernfs_new

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Message-ID: <20190416144617.GA349476@devbig004.ftw2.facebook.com>
Date:   Tue, 16 Apr 2019 07:47:30 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernfs: fix barrier usage in __kernfs_new_node()

On Tue, Apr 16, 2019 at 02:17:11PM +0200, Andrea Parri wrote:
> smp_mb__before_atomic() can not be applied to atomic_set().  Remove the
> barrier and rely on RELEASE synchronization.
> 
> Fixes: ba16b2846a8c6 ("kernfs: add an API to get kernfs node from inode number")
> Cc: stable@...r.kernel.org
> Signed-off-by: Andrea Parri <andrea.parri@...rulasolutions.com>
> ---
>  fs/kernfs/dir.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index b84d635567d38..1e7a74b8e0647 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -650,11 +650,10 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
>  	kn->id.generation = gen;
>  
>  	/*
> -	 * set ino first. This barrier is paired with atomic_inc_not_zero in
> +	 * set ino first. This RELEASE is paired with atomic_inc_not_zero in
>  	 * kernfs_find_and_get_node_by_ino
>  	 */
> -	smp_mb__before_atomic();
> -	atomic_set(&kn->count, 1);
> +	atomic_set_release(&kn->count, 1);

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

Thanks.

--
tejun