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mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected()

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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: 36e66c554b ("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>
This commit is contained in:
SeongJae Park 2022-12-28 17:59:42 +00:00 committed by Andrew Morton
parent 3783e1721b
commit 01b5022f0a
1 changed files with 4 additions and 2 deletions
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6
mm/page_reporting.c
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@ -356,7 +356,8 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
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 page_reporting_dev_info *prdev)
{
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();