+ mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch added to mm-unstable branch

+ mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch

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

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------------------------------------------------------
From: SeongJae Park <sj@kernel.org>
Subject: mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected()
Date: Wed, 28 Dec 2022 17:59:42 +0000

Page reporting fetches pr_dev_info using rcu_access_pointer(), which is
for safely fetching a pointer that will not be dereferenced but could
concurrently updated.  The code indeed does not dereference pr_dev_info
after fetching it using rcu_access_pointer(), but it fetches the pointer
while concurrent updates to the pointer is avoided by holding the update
side lock, page_reporting_mutex.

In the case, rcu_dereference_protected() should be used instead because it
provides better readability and performance on some cases, as
rcu_dereference_protected() avoids use of READ_ONCE().  Replace the
rcu_access_pointer() calls with rcu_dereference_protected().

Link: https://lkml.kernel.org/r/20221228175942.149491-1-sj@kernel.org
Fixes: 36e66c554b5c ("mm: introduce Reported pages")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/page_reporting.c~mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected
+++ a/mm/page_reporting.c
@@ -356,7 +356,8 @@ int page_reporting_register(struct page_
 	mutex_lock(&page_reporting_mutex);
 
 	/* nothing to do if already in use */
-	if (rcu_access_pointer(pr_dev_info)) {
+	if (rcu_dereference_protected(pr_dev_info,
+				lockdep_is_held(&page_reporting_mutex))) {
 		err = -EBUSY;
 		goto err_out;
 	}
@@ -401,7 +402,8 @@ void page_reporting_unregister(struct pa
 {
 	mutex_lock(&page_reporting_mutex);
 
-	if (rcu_access_pointer(pr_dev_info) == prdev) {
+	if (prdev == rcu_dereference_protected(pr_dev_info,
+				lockdep_is_held(&page_reporting_mutex))) {
 		/* Disable page reporting notification */
 		RCU_INIT_POINTER(pr_dev_info, NULL);
 		synchronize_rcu();
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-core-implement-damos-filter.patch
mm-damon-paddr-support-damos-filters.patch
mm-damon-reclaim-add-a-parameter-called-skip_anon-for-avoiding-anonymous-pages-reclamation.patch
docs-admin-guide-damon-reclaim-document-skip_anon-parameter.patch
mm-damon-sysfs-schemes-implement-filters-directory.patch
mm-damon-sysfs-schemes-implement-filter-directory.patch
mm-damon-sysfs-schemes-connect-filter-directory-and-filters-directory.patch
mm-damon-sysfs-schemes-implement-scheme-filters.patch
mm-damon-sysfs-schemes-implement-scheme-filters-fix.patch
mm-damon-sysfs-schemes-implement-scheme-filters-fix-fix-2.patch
selftests-damon-sysfs-test-filters-directory.patch
docs-admin-guide-mm-damon-usage-document-damos-filters-of-sysfs.patch
docs-abi-damon-document-scheme-filters-files.patch
mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch