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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Bob Peterson <rpeterso@redhat.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        cluster-devel@redhat.com, linux-kernel@vger.kernel.org,
        Deepak R Varma <drv@mailo.com>
Cc:     Ira Weiny <ira.weiny@intel.com>,
        Sumitra Sharma <sumitraartsy@gmail.com>,
        Deepak R Varma <drv@mailo.com>
Subject: Re: [PATCH v3 4/6] gfs2: Replace kmap_atomic() by kmap_local_page() in lops.c
Date:   Sat, 01 Jul 2023 15:16:48 +0200
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In-Reply-To: <4817527acb9e015b3c6929517993ea50ba3427ad.1688073459.git.drv@mailo.com>
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 <4817527acb9e015b3c6929517993ea50ba3427ad.1688073459.git.drv@mailo.com>
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On gioved=EC 29 giugno 2023 23:51:17 CEST Deepak R Varma wrote:
> kmap_atomic() is deprecated in favor of kmap_local_{folio,page}().

Deepak,

Can you please add a reference to the highmem documentation and to the patc=
h=20
from Ira that added a deprecation check for kmap() and kmap_atomic() in his=
=20
commit regarding checkpatch.pl?

There may be maintainers / reviewers who are still unaware of this=20
information. It would surely help them with reviewing. Furthermore it might=
=20
suggest maintainers to convert their subsystem / driver to the new API or=20
remove and use plain page_address() (if it is possible to prove that pages=
=20
can't come from ZONE_HIGHMEM).

>=20
> Therefore, replace kmap_atomic() with kmap_local_page() in following
> functions of lops.c:
>    - gfs2_jhead_pg_srch()
>    - gfs2_check_magic()
>    - gfs2_before_commit()
>=20
> kmap_atomic() disables page-faults and preemption (the latter only for
> !PREEMPT_RT kernels), However, the code within the mapping/un-mapping in
> stuffed_readpage() does not depend on the above-mentioned side effects.
>=20
> 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()).
>=20
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> Signed-off-by: Deepak R Varma <drv@mailo.com>
> ---
> Changes in v3:
>    - Patch included in patch series
>=20
> Changes in v2:
>    - None
>=20
>=20
>  fs/gfs2/lops.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>=20
> diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
> index 1902413d5d12..a7c2296cb3c6 100644
> --- a/fs/gfs2/lops.c
> +++ b/fs/gfs2/lops.c
> @@ -427,7 +427,7 @@ static bool gfs2_jhead_pg_srch(struct gfs2_jdesc *jd,
>  {
>  	struct gfs2_sbd *sdp =3D GFS2_SB(jd->jd_inode);
>  	struct gfs2_log_header_host lh;
> -	void *kaddr =3D kmap_atomic(page);
> +	void *kaddr =3D kmap_local_page(page);
>  	unsigned int offset;
>  	bool ret =3D false;
>
Deepak,

Are we mixing declarations with functions calls? Is it good practice? If no=
t,=20
I'd suggest to move the mapping to a better suited place.
>=20
> @@ -441,7 +441,7 @@ static bool gfs2_jhead_pg_srch(struct gfs2_jdesc *jd,
>  			}
>  		}
>  	}
> -	kunmap_atomic(kaddr);
> +	kunmap_local(kaddr);
>  	return ret;
>  }
>=20
> @@ -626,11 +626,11 @@ static void gfs2_check_magic(struct buffer_head *bh)
>  	__be32 *ptr;
>=20
>  	clear_buffer_escaped(bh);
> -	kaddr =3D kmap_atomic(bh->b_page);
> +	kaddr =3D kmap_local_page(bh->b_page);
>  	ptr =3D kaddr + bh_offset(bh);
>  	if (*ptr =3D=3D cpu_to_be32(GFS2_MAGIC))
>  		set_buffer_escaped(bh);
> -	kunmap_atomic(kaddr);
> +	kunmap_local(kaddr);
>  }
>=20
>  static int blocknr_cmp(void *priv, const struct list_head *a,
> @@ -699,10 +699,10 @@ static void gfs2_before_commit(struct gfs2_sbd *sdp,
> unsigned int limit, void *kaddr;
>  				page =3D mempool_alloc(gfs2_page_pool,=20
GFP_NOIO);
>  				ptr =3D page_address(page);
> -				kaddr =3D kmap_atomic(bd2->bd_bh-
>b_page);
> +				kaddr =3D kmap_local_page(bd2->bd_bh-
>b_page);
>  				memcpy(ptr, kaddr + bh_offset(bd2-
>bd_bh),
>  				       bd2->bd_bh->b_size);
>
Deepak,

How about memcpy_from_page()?

Thanks,

=46abio
>
> -				kunmap_atomic(kaddr);
> +				kunmap_local(kaddr);
>  				*(__be32 *)ptr =3D 0;
>  				clear_buffer_escaped(bd2->bd_bh);
>  				unlock_buffer(bd2->bd_bh);
> --
> 2.34.1