cachestat-do-not-flush-stats-in-recency-check.patch removed from -mm tree

merged mm-hotfixes-stable Andrew Morton 1 participant 1 message Jul 4, 2024 Stable branch

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Andrew Morton

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2024-07-04 05:42 UTC #0 lore raw

The quilt patch titled
Subject: cachestat: do not flush stats in recency check
has been removed from the -mm tree. Its filename was
cachestat-do-not-flush-stats-in-recency-check.patch

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

------------------------------------------------------
From: Nhat Pham <[email protected]>
Subject: cachestat: do not flush stats in recency check
Date: Thu, 27 Jun 2024 13:17:37 -0700

syzbot detects that cachestat() is flushing stats, which can sleep, in its RCU read section (see [1]). This is done in the workingset_test_recent() step (which checks if the folio's eviction is recent).

Move the stat flushing step to before the RCU read section of cachestat, and skip stat flushing during the recency check.

[1]: https://lore.kernel.org/cgroups/[email protected]/

Link https://lkml.kernel.org/r/[email protected] open here

Fixes b00684722262 ("mm: workingset: move the stats flush into workingset_test_recent()")

Signed-off-by Nhat Pham <[email protected]>

Reported-by [email protected]

Closes https://lore.kernel.org/cgroups/[email protected]/ open here

Debugged-by Johannes Weiner <[email protected]>

Acked-by Johannes Weiner <[email protected]>

Acked-by Shakeel Butt <[email protected]>

Cc Al Viro <[email protected]>

Cc David Hildenbrand <[email protected]>

Cc "Huang, Ying" <[email protected]>

Cc Kairui Song <[email protected]>

Cc Matthew Wilcox (Oracle) <[email protected]>

Cc Ryan Roberts <[email protected]>

Cc Yosry Ahmed <[email protected]>

Cc <[email protected]> [6.8+]

Signed-off-by Andrew Morton <[email protected]>

---

 include/linux/swap.h |    3 ++-
 mm/filemap.c         |    5 ++++-
 mm/workingset.c      |   14 +++++++++++---
 3 files changed, 17 insertions(+), 5 deletions(-)

include/linux/swap.h renamed from include/linux/swap.h~cachestat-do-not-flush-stats-in-recency-check +2 -1

@@ -354,7 +354,8 @@ static inline swp_entry_t page_swap_entr
 }
 
 /* linux/mm/workingset.c */
-bool workingset_test_recent(void *shadow, bool file, bool *workingset);
+bool workingset_test_recent(void *shadow, bool file, bool *workingset,
+				bool flush);
 void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages);
 void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg);
 void workingset_refault(struct folio *folio, void *shadow);

mm/filemap.c renamed from mm/filemap.c~cachestat-do-not-flush-stats-in-recency-check +4 -1

@@ -4248,6 +4248,9 @@ static void filemap_cachestat(struct add
 	XA_STATE(xas, &mapping->i_pages, first_index);
 	struct folio *folio;
 
+	/* Flush stats (and potentially sleep) outside the RCU read section. */
+	mem_cgroup_flush_stats_ratelimited(NULL);
+
 	rcu_read_lock();
 	xas_for_each(&xas, folio, last_index) {
 		int order;

@@ -4311,7 +4314,7 @@ static void filemap_cachestat(struct add
 					goto resched;
 			}
 #endif
-			if (workingset_test_recent(shadow, true, &workingset))
+			if (workingset_test_recent(shadow, true, &workingset, false))
 				cs->nr_recently_evicted += nr_pages;
 
 			goto resched;

mm/workingset.c renamed from mm/workingset.c~cachestat-do-not-flush-stats-in-recency-check +11 -3

@@ -412,10 +412,12 @@ void *workingset_eviction(struct folio *
  * @file: whether the corresponding folio is from the file lru.
  * @workingset: where the workingset value unpacked from shadow should
  * be stored.
+ * @flush: whether to flush cgroup rstat.
  *
  * Return: true if the shadow is for a recently evicted folio; false otherwise.
  */
-bool workingset_test_recent(void *shadow, bool file, bool *workingset)
+bool workingset_test_recent(void *shadow, bool file, bool *workingset,
+				bool flush)
 {
 	struct mem_cgroup *eviction_memcg;
 	struct lruvec *eviction_lruvec;

@@ -467,10 +469,16 @@ bool workingset_test_recent(void *shadow
 
 	/*
 	 * Flush stats (and potentially sleep) outside the RCU read section.
+	 *
+	 * Note that workingset_test_recent() itself might be called in RCU read
+	 * section (for e.g, in cachestat) - these callers need to skip flushing
+	 * stats (via the flush argument).
+	 *
 	 * XXX: With per-memcg flushing and thresholding, is ratelimiting
 	 * still needed here?
 	 */
-	mem_cgroup_flush_stats_ratelimited(eviction_memcg);
+	if (flush)
+		mem_cgroup_flush_stats_ratelimited(eviction_memcg);
 
 	eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
 	refault = atomic_long_read(&eviction_lruvec->nonresident_age);

@@ -558,7 +566,7 @@ void workingset_refault(struct folio *fo
 
 	mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
 
-	if (!workingset_test_recent(shadow, file, &workingset))
+	if (!workingset_test_recent(shadow, file, &workingset, true))
 		return;
 
 	folio_set_active(folio);

Patches currently in -mm which might be from [email protected] are