linux-kernel - [PATCH] NFS: Convert kmap_atomic() to kmap_local

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Date:   Wed,  3 May 2023 19:24:11 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH] NFS: Convert kmap_atomic() to kmap_local_folio()

kmap_atomic() is deprecated in favor of kmap_local_{folio,page}().

Therefore, replace kmap_atomic() with kmap_local_folio() in
nfs_readdir_folio_array_append().

kmap_atomic() disables page-faults and preemption (the latter only for
!PREEMPT_RT kernels), However, the code within the mapping/un-mapping in
nfs_readdir_folio_array_append() 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()).

Tested with (x)fstests in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel
with HIGHMEM64GB enabled.

Cc: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---

"./check -nfs -g quick", with or without this patch, always fails the
same 12 tests of 559: generic/053 generic/099 generic/105 generic/193
generic/294 generic/318 generic/319 generic/444 generic/465 generic/528
generic/529 generic/531.

Therefore, I think I can say that this patch does not introduce any
regressions.

 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 8257de6dba45..8fa8ae49d6cd 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -317,7 +317,7 @@ static int nfs_readdir_folio_array_append(struct folio *folio,

 	name = nfs_readdir_copy_name(entry->name, entry->len);

-	array = kmap_atomic(folio_page(folio, 0));
+	array = kmap_local_folio(folio, 0);
 	if (!name)
 		goto out;
 	ret = nfs_readdir_array_can_expand(array);
@@ -340,7 +340,7 @@ static int nfs_readdir_folio_array_append(struct folio *folio,
 		nfs_readdir_array_set_eof(array);
 out:
 	*cookie = array->last_cookie;
-	kunmap_atomic(array);
+	kunmap_local(array);
 	return ret;
 }

-- 
2.40.0