linux-kernel - Re: [PATCH v2] gfs2: Replace deprecated kmap_atomic() by kmap_local

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Date:   Tue, 27 Jun 2023 13:41:59 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Bob Peterson <rpeterso@...hat.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        cluster-devel@...hat.com, linux-kernel@...r.kernel.org,
        Deepak R Varma <drv@...lo.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Sumitra Sharma <sumitraartsy@...il.com>,
        Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH v2] gfs2: Replace deprecated kmap_atomic() by kmap_local_page()

On lunedì 26 giugno 2023 08:51:09 CEST Deepak R Varma wrote:
> kmap_atomic() is deprecated in favor of kmap_local_{folio,page}().
> 
> Therefore, replace kmap_atomic() with kmap_local_page() in
> gfs2_internal_read() and stuffed_readpage().
> 
> kmap_atomic() disables page-faults and preemption (the latter only for
> !PREEMPT_RT kernels), However, the code within the mapping/un-mapping in
> gfs2_internal_read() and stuffed_readpage() does not depend on the
> above-mentioned side effects.
> 
> Therefore, a mere replacement of the old API with the new one is all that
> is required (i.e., there is no need to explicitly add any calls to
> pagefault_disable() and/or preempt_disable()).
> 
> Signed-off-by: Deepak R Varma <drv@...lo.com>
> ---
> Note: The Patch is build tested only. I will be happy to run recommended
> testing with some guidance if required.
> 
> Changes in v2:
>    - Update patch description to correct the replacement function name from
>      kmap_local_folio to kmap_local _page

Ah, well done. I didn't note this with the comment on v1.
 
>  fs/gfs2/aops.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
> index 3b41542d6697..7bd92054d353 100644
> --- a/fs/gfs2/aops.c
> +++ b/fs/gfs2/aops.c
> @@ -432,10 +432,10 @@ static int stuffed_readpage(struct gfs2_inode *ip,
> struct page *page) if (error)
>  		return error;
> 
> -	kaddr = kmap_atomic(page);
> +	kaddr = kmap_local_page(page);
>  	memcpy(kaddr, dibh->b_data + sizeof(struct gfs2_dinode), dsize);
>  	memset(kaddr + dsize, 0, PAGE_SIZE - dsize);
> -	kunmap_atomic(kaddr);
> +	kunmap_local(kaddr);
>  	flush_dcache_page(page);
>  	brelse(dibh);
>  	SetPageUptodate(page);
> @@ -498,12 +498,12 @@ int gfs2_internal_read(struct gfs2_inode *ip, char 
*buf,
> loff_t *pos, continue;
>  			return PTR_ERR(page);
>  		}
> -		p = kmap_atomic(page);
> +		p = kmap_local_page(page);
>  		amt = size - copied;
>  		if (offset + size > PAGE_SIZE)
>  			amt = PAGE_SIZE - offset;
>  		memcpy(buf + copied, p + offset, amt);

As said in the comment on v1, the memcpy_from_page() helper is better suited 
here, unless you noted something that prevents its use and that I'm not able 
to see at the moment.

Thanks,

Fabio

> -		kunmap_atomic(p);
> +		kunmap_local(p);
>  		put_page(page);
>  		copied += amt;
>  		index++;
> --
> 2.34.1