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cachestat: do not flush stats in recency check

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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: b006847222 ("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>
This commit is contained in:
Nhat Pham 2024-06-27 13:17:37 -07:00 committed by Andrew Morton
parent 9fd154ba92
commit 5a4d8944d6
3 changed files with 17 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/swap.h
View File

@ -354,7 +354,8 @@ static inline swp_entry_t page_swap_entry(struct page *page)
}
/* 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);

5
mm/filemap.c
View File

@ -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;

14
mm/workingset.c
View File

@ -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);