[merged mm-stable] mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch removed from -mm tree

[merged mm-stable] mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected()
has been removed from the -mm tree.  Its filename was
     mm-page_reporting-replace-rcu_access_pointer-with-rcu_dereference_protected.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
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>
---

 mm/page_reporting.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- 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-update-kernel-doc-comments-for-damos-action-supports-of-each-damon-operations-set.patch
mm-damon-core-update-kernel-doc-comments-for-damos-filters-supports-of-each-damon-operations-set.patch
docs-mm-damon-index-mention-damos-on-the-intro.patch
docs-admin-guide-mm-damon-usage-update-damos-actions-filters-supports-of-each-damon-operations-set.patch
docs-mm-damon-add-a-maintainer-profile-for-damon.patch
maintainers-damon-link-maintainer-profile-git-trees-and-website.patch
selftests-damon-sysfs-hide-expected-write-failures.patch
selftests-damon-debugfs_rm_non_contexts-hide-expected-write-error-messages.patch
scripts-spelling-add-a-few-more-typos.patch