[PATCH] fs/ext2: Replace kmap_atomic() with kmap_local_page()

Fabio M. De Francesco
2022-12-31T17:42:15Z

kmap_atomic() is deprecated in favor of kmap_local_page(). Therefore,
replace kmap_atomic() with kmap_local_page().

kmap_atomic() is implemented like a kmap_local_page() which also disables
page-faults and preemption (the latter only for !PREEMPT_RT kernels).

However, the code within the mapping and un-mapping in ext2_make_empty()
does not depend on the above-mentioned side effects.

Therefore, a mere replacement of the old API with the new one is all it
is required (i.e., there is no need to explicitly add any calls to
pagefault_disable() and/or preempt_disable()).

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---

I tried my best to understand the code within mapping and un-mapping.
However, I'm not an expert. Therefore, although I'm pretty confident, I
cannot be 100% sure that the code between the mapping and the un-mapping
does not depend on pagefault_disable() and/or preempt_disable().

Unfortunately, I cannot currently test this changes to check the
above-mentioned assumptions. However, if I'm required to do the tests
with (x)fstests, I have no problems with doing them in the next days.

If so, I'll test in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with
HIGHMEM64GB enabled.

I'd like to hear whether or not the maintainers require these tests
and/or other tests.

fs/ext2/dir.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
index e5cbc27ba459..0f144c5c7861 100644
--- a/fs/ext2/dir.c
+++ b/fs/ext2/dir.c
@@ -646,7 +646,7 @@ int ext2_make_empty(struct inode *inode, struct inode *parent)
unlock_page(page);
goto fail;
}
- kaddr = kmap_atomic(page);
+ kaddr = kmap_local_page(page);
memset(kaddr, 0, chunk_size);
de = (struct ext2_dir_entry_2 *)kaddr;
de->name_len = 1;
@@ -661,7 +661,7 @@ int ext2_make_empty(struct inode *inode, struct inode *parent)
de->inode = cpu_to_le32(parent->i_ino);
memcpy (de->name, "..\0", 4);
ext2_set_de_type (de, inode);
- kunmap_atomic(kaddr);
+ kunmap_local(kaddr);
ext2_commit_chunk(page, 0, chunk_size);
err = ext2_handle_dirsync(inode);
fail:
--
2.39.0