linux-kernel - Re: [PATCH] zsmalloc: Delete an unnecessary check before the function call "iput"

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Message-ID: <20160725004956.GA430@swordfish>
Date:	Mon, 25 Jul 2016 09:49:56 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	linux-mm@...ck.org, Minchan Kim <minchan@...nel.org>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] zsmalloc: Delete an unnecessary check before the
 function call "iput"

On (07/22/16 20:02), SF Markus Elfring wrote:
> The iput() function tests whether its argument is NULL and then
> returns immediately. Thus the test around the call is not needed.
> 
> This issue was detected by using the Coccinelle software.

there is no issue; the change is just cosmetic.


> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>



alloc_anon_inode() returns ERR_PTR, so I'd probably rather
change iput() to do IS_ERR_OR_NULL instead of !NULL.

	inode = alloc_anon_inode();
	if (IS_ERR(inode)) {
		inode = NULL;
		^^^^^^^^^^^^^
	}
	...
	iput(inode);

this NULL assignment on error path is a bit fragile.

IOW, something like this

---

diff --git a/fs/inode.c b/fs/inode.c
index 559a9da..f1b7bd2 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1497,7 +1497,7 @@ static void iput_final(struct inode *inode)
  */
 void iput(struct inode *inode)
 {
-       if (!inode)
+       if (IS_ERR_OR_NULL(inode))
                return;
        BUG_ON(inode->i_state & I_CLEAR);
 retry:


---

	-ss

> ---
>  mm/zsmalloc.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 5e5237c..7b5fd2b 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -2181,8 +2181,7 @@ static int zs_register_migration(struct zs_pool *pool)
>  static void zs_unregister_migration(struct zs_pool *pool)
>  {
>  	flush_work(&pool->free_work);
> -	if (pool->inode)
> -		iput(pool->inode);
> +	iput(pool->inode);
>  }
>  
>  /*
> -- 
> 2.9.2
>