Messages in this thread Patch in this message | | | From | SeongJae Park <> | Subject | [PATCH v3] mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected() | Date | Wed, 28 Dec 2022 17:59:42 +0000 |
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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().
Fixes: 36e66c554b5c ("mm: introduce Reported pages") Signed-off-by: SeongJae Park <sj@kernel.org> --- Changes from v2 (https://lore.kernel.org/linux-mm/20221228012902.1510901-1-sj@kernel.org/) - Fix typos (Miaohe Lin) - Add Fixes: tag
Changes from v1 (https://lore.kernel.org/linux-mm/20221227192158.2553-1-sj@kernel.org/) - Explicitly set the protection condition (Matthew Wilcox)
mm/page_reporting.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/mm/page_reporting.c b/mm/page_reporting.c index 79a8554f024c..c65813a9dc78 100644 --- a/mm/page_reporting.c +++ b/mm/page_reporting.c @@ -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(); -- 2.25.1
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