linux-kernel - Re: [PATCH] NFS: check the return value of mempool

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Message-id: <164806948116.6096.12331736937963571485@noble.neil.brown.name>
Date:   Thu, 24 Mar 2022 08:04:41 +1100
From:   "NeilBrown" <neilb@...e.de>
To:     xkernel.wang@...mail.com
Cc:     trond.myklebust@...merspace.com, anna.schumaker@...app.com,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Xiaoke Wang" <xkernel.wang@...mail.com>
Subject: Re: [PATCH] NFS: check the return value of mempool_alloc()

On Wed, 23 Mar 2022, xkernel.wang@...mail.com wrote:
> From: Xiaoke Wang <xkernel.wang@...mail.com>
> 
> The check was first removed in 518662e ("NFS: fix usage of mempools.")
> as the passed GFP flags is `GFP_NOIO`.
> While now the flag is changed to `GFP_KERNEL` by 2b17d72 ("NFS: Clean
> up writeback code"), so it is better to check it.

no.  GFP_KERNEL is not that different from GFP_NOIO.

mempool_alloc() can only fail with __GFP_DIRECT_RECLAIM is not passed.

Please try to understand the code before you change it.

NeilBrown


> 
> Signed-off-by: Xiaoke Wang <xkernel.wang@...mail.com>
> ---
>  fs/nfs/write.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> index eae9bf1..831fad9 100644
> --- a/fs/nfs/write.c
> +++ b/fs/nfs/write.c
> @@ -106,8 +106,10 @@ static struct nfs_pgio_header *nfs_writehdr_alloc(void)
>  {
>  	struct nfs_pgio_header *p = mempool_alloc(nfs_wdata_mempool, GFP_KERNEL);
>  
> -	memset(p, 0, sizeof(*p));
> -	p->rw_mode = FMODE_WRITE;
> +	if (p) {
> +		memset(p, 0, sizeof(*p));
> +		p->rw_mode = FMODE_WRITE;
> +	}
>  	return p;
>  }
>  
> -- 
> 
>