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@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: 36e66c554b5c ("mm: introduce Reported pages")
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- 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@xxxxxxxxxx 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
