+ hfs-unmap-the-page-in-the-fail_page-label.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: hfs: unmap the page in the "fail_page" label
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     hfs-unmap-the-page-in-the-fail_page-label.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hfs-unmap-the-page-in-the-fail_page-label.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Subject: hfs: unmap the page in the "fail_page" label
Date: Sun, 21 Aug 2022 20:03:58 +0200

Patch series "hfs: Replace kmap() with kmap_local_page()".

kmap() is being deprecated in favor of kmap_local_page().

There are two main problems with kmap(): (1) It comes with an overhead as
mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmaps pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts). 
It is faster than kmap() in kernels with HIGHMEM enabled.  Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored and still valid.

Since its use in fs/hfs is safe everywhere, it should be preferred.

Therefore, replace kmap() with kmap_local_page() in fs/hfs.  Where
possible, use the suited standard helpers (memzero_page(), memcpy_page())
instead of open coding kmap_local_page() plus memset() or memcpy().

Fix a bug due to a page being not unmapped if the code jumps to the
"fail_page" label (1/3).

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


This patch (of 3):

Several paths within hfs_btree_open() jump to the "fail_page" label where
put_page() is called while the page is still mapped.

Call kunmap() to unmap the page soon before put_page().

Link: https://lkml.kernel.org/r/20220821180400.8198-1-fmdefrancesco@gmail.com
Link: https://lkml.kernel.org/r/20220821180400.8198-2-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Cc: Christian Brauner (Microsoft) <brauner@kernel.org>
Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Matthew Wilcox <willy@infradead.org>]
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/hfs/btree.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/hfs/btree.c~hfs-unmap-the-page-in-the-fail_page-label
+++ a/fs/hfs/btree.c
@@ -124,6 +124,7 @@ struct hfs_btree *hfs_btree_open(struct
 	return tree;
 
 fail_page:
+	kunmap(page);
 	put_page(page);
 free_inode:
 	tree->inode->i_mapping->a_ops = &hfs_aops;
_

Patches currently in -mm which might be from fmdefrancesco@gmail.com are

hfsplus-unmap-the-page-in-the-fail_page-label.patch
hfsplus-convert-kmap-to-kmap_local_page-in-bnodec.patch
hfsplus-convert-kmap-to-kmap_local_page-in-bitmapc.patch
hfsplus-convert-kmap-to-kmap_local_page-in-btreec.patch
fs-isofs-replace-kmap-with-kmap_local_page.patch
kexec-replace-kmap-with-kmap_local_page.patch
hfs-unmap-the-page-in-the-fail_page-label.patch
hfs-replace-kmap-with-kmap_local_page-in-bnodec.patch
hfs-replace-kmap-with-kmap_local_page-in-btreec.patch