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authorNhat Pham2024-06-27 13:17:37 -0700
committerAndrew Morton2024-07-03 22:40:37 -0700
commit5a4d8944d6b1e1aaaa83ea42c116b520b4ed0394 (patch)
tree9fb61c0a8348764dfa6aa92695533a252fb6a116 /mm
parent9fd154ba926b34c833b7bfc4c14ee2e931b3d743 (diff)
cachestat: do not flush stats in recency check
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/000000000000f71227061bdf97e0@google.com/ Link: https://lkml.kernel.org/r/20240627201737.3506959-1-nphamcs@gmail.com Fixes: b00684722262 ("mm: workingset: move the stats flush into workingset_test_recent()") Signed-off-by: Nhat Pham <nphamcs@gmail.com> Reported-by: syzbot+b7f13b2d0cc156edf61a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/cgroups/000000000000f71227061bdf97e0@google.com/ Debugged-by: Johannes Weiner <hannes@cmpxchg.org> Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Shakeel Butt <shakeel.butt@linux.dev> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: David Hildenbrand <david@redhat.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Kairui Song <kasong@tencent.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Yosry Ahmed <yosryahmed@google.com> Cc: <stable@vger.kernel.org> [6.8+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/filemap.c5
-rw-r--r--mm/workingset.c14
2 files changed, 15 insertions, 4 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index fedefb10d947..298485d4b992 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4248,6 +4248,9 @@ static void filemap_cachestat(struct address_space *mapping,
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 address_space *mapping,
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;
diff --git a/mm/workingset.c b/mm/workingset.c
index c22adb93622a..a2b28e356e68 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -412,10 +412,12 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
* @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, bool file, bool *workingset)
/*
* 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 *folio, void *shadow)
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);