linux-kernel - Re: [PATCH] nfs: Replace kmap() with kmap_local

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Message-ID: <Yr9C1h8fIAneJ9MU@iweiny-desk3>
Date:   Fri, 1 Jul 2022 11:54:14 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
CC:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Kees Cook <keescook@...omium.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Baptiste Lepers <baptiste.lepers@...il.com>,
        <linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nfs: Replace kmap() with kmap_local_page()

On Tue, Jun 28, 2022 at 08:24:26PM +0200, Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page().
> 
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Furthermore, the mapping can be acquired from any context
> (including interrupts).
> 
> Therefore, use kmap_local_page() in nfs_do_filldir() because this mapping
> is per thread, CPU local, and not globally visible.
> 
> Suggested-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
> 
> I cannot test this patch for several reasons. While these changes seem safe
> and trivial, I would feel better if people familiar with NFS could take the
> time to properly test this patch. Thank you.
> 
>  fs/nfs/dir.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 0c4e8dd6aa96..8b89f10d8899 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -1084,7 +1084,7 @@ static void nfs_do_filldir(struct nfs_readdir_descriptor *desc,
>  	struct nfs_cache_array *array;
>  	unsigned int i;
>  
> -	array = kmap(desc->page);
> +	array = kmap_local_page(desc->page);
>  	for (i = desc->cache_entry_index; i < array->size; i++) {
>  		struct nfs_cache_array_entry *ent;
>  
> @@ -1110,7 +1110,7 @@ static void nfs_do_filldir(struct nfs_readdir_descriptor *desc,
>  	if (array->page_is_eof)
>  		desc->eof = !desc->eob;
>  
> -	kunmap(desc->page);
> +	kunmap_local(array);
>  	dfprintk(DIRCACHE, "NFS: nfs_do_filldir() filling ended @ cookie %llu\n",
>  			(unsigned long long)desc->dir_cookie);
>  }
> -- 
> 2.36.1
>