linux-kernel - Re: [PATCH v3 2/2] fscache: Use clear_and_wake_up_bit() in fscache_create_volume

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Message-ID: <bc07b4d69f6c709988d2faca50717a402c1ed81e.camel@kernel.org>
Date:   Fri, 13 Jan 2023 10:28:01 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     Hou Tao <houtao@...weicloud.com>, linux-cachefs@...hat.com
Cc:     David Howells <dhowells@...hat.com>, linux-erofs@...ts.ozlabs.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jingbo Xu <jefflexu@...ux.alibaba.com>, houtao1@...wei.com
Subject: Re: [PATCH v3 2/2] fscache: Use clear_and_wake_up_bit() in
 fscache_create_volume_work()

On Fri, 2023-01-13 at 19:52 +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@...wei.com>
> 
> fscache_create_volume_work() uses wake_up_bit() to wake up the processes
> which are waiting for the completion of volume creation. According to
> comments in wake_up_bit() and waitqueue_active(), an extra smp_mb() is
> needed to guarantee the memory order between FSCACHE_VOLUME_CREATING
> flag and waitqueue_active() before invoking wake_up_bit().
> 
> Fixing it by using clear_and_wake_up_bit() to add the missing memory
> barrier.
> 
> Reviewed-by: Jingbo Xu <jefflexu@...ux.alibaba.com>
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>  fs/fscache/volume.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c
> index 903af9d85f8b..cdf991bdd9de 100644
> --- a/fs/fscache/volume.c
> +++ b/fs/fscache/volume.c
> @@ -280,8 +280,7 @@ static void fscache_create_volume_work(struct work_struct *work)
>  	fscache_end_cache_access(volume->cache,
>  				 fscache_access_acquire_volume_end);
>  
> -	clear_bit_unlock(FSCACHE_VOLUME_CREATING, &volume->flags);
> -	wake_up_bit(&volume->flags, FSCACHE_VOLUME_CREATING);
> +	clear_and_wake_up_bit(FSCACHE_VOLUME_CREATING, &volume->flags);
>  	fscache_put_volume(volume, fscache_volume_put_create_work);
>  }
>  

Reviewed-by: Jeff Layton <jlayton@...nel.org>