linux-kernel - Re: [PATCH] xfs: Use refcount_t instead of atomic_t for xmi

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Message-ID: <20250106195151.GJ6174@frogsfrogsfrogs>
Date: Mon, 6 Jan 2025 11:51:51 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Pei Xiao <xiaopei01@...inos.cn>
Cc: cem@...nel.org, linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] xfs: Use refcount_t instead of atomic_t for xmi_refcount

On Mon, Dec 30, 2024 at 03:18:16PM +0800, Pei Xiao wrote:
> Use an API that resembles more the actual use of xmi_refcount.
> 
> Found by cocci:
>     fs/xfs/xfs_exchmaps_item.c:57:5-24: WARNING: atomic_dec_and_test
> variation before object free at line 58.
> 
> Fixes: 6c08f434bd33 ("xfs: introduce a file mapping exchange log intent item")
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202412260634.uSDUNyYS-lkp@intel.com/
> Signed-off-by: Pei Xiao <xiaopei01@...inos.cn>

What has changed since
https://lore.kernel.org/linux-xfs/1508497678-10508-1-git-send-email-elena.reshetova@intel.com/
and if something has, why wouldn't you apply atomic_t -> refcount_t for
/all/ the log intent item types?

--D

> ---
>  fs/xfs/xfs_exchmaps_item.c | 6 +++---
>  fs/xfs/xfs_exchmaps_item.h | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_exchmaps_item.c b/fs/xfs/xfs_exchmaps_item.c
> index 264a121c5e16..5975a16c54e3 100644
> --- a/fs/xfs/xfs_exchmaps_item.c
> +++ b/fs/xfs/xfs_exchmaps_item.c
> @@ -57,8 +57,8 @@ STATIC void
>  xfs_xmi_release(
>  	struct xfs_xmi_log_item	*xmi_lip)
>  {
> -	ASSERT(atomic_read(&xmi_lip->xmi_refcount) > 0);
> -	if (atomic_dec_and_test(&xmi_lip->xmi_refcount)) {
> +	ASSERT(refcount_read(&xmi_lip->xmi_refcount) > 0);
> +	if (refcount_dec_and_test(&xmi_lip->xmi_refcount)) {
>  		xfs_trans_ail_delete(&xmi_lip->xmi_item, 0);
>  		xfs_xmi_item_free(xmi_lip);
>  	}
> @@ -138,7 +138,7 @@ xfs_xmi_init(
>  
>  	xfs_log_item_init(mp, &xmi_lip->xmi_item, XFS_LI_XMI, &xfs_xmi_item_ops);
>  	xmi_lip->xmi_format.xmi_id = (uintptr_t)(void *)xmi_lip;
> -	atomic_set(&xmi_lip->xmi_refcount, 2);
> +	refcount_set(&xmi_lip->xmi_refcount, 2);
>  
>  	return xmi_lip;
>  }
> diff --git a/fs/xfs/xfs_exchmaps_item.h b/fs/xfs/xfs_exchmaps_item.h
> index efa368d25d09..b8be3bca3155 100644
> --- a/fs/xfs/xfs_exchmaps_item.h
> +++ b/fs/xfs/xfs_exchmaps_item.h
> @@ -38,7 +38,7 @@ struct kmem_cache;
>   */
>  struct xfs_xmi_log_item {
>  	struct xfs_log_item		xmi_item;
> -	atomic_t			xmi_refcount;
> +	refcount_t			xmi_refcount;
>  	struct xfs_xmi_log_format	xmi_format;
>  };
>  
> -- 
> 2.25.1
> 
>