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mm: annotate data-race in cpu_needs_drain()

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KCSAN reports a data-race when cpu_needs_drain() reads another CPU's
per-cpu folio_batch->nr without locking, while the owning CPU writes to it
via folio_batch_add().

Reading a slightly stale value is harmless -- cpu_needs_drain() only
decides whether to schedule a drain, and the next iteration of
__lru_add_drain_all() will re-check.  Use data_race() to annotate the
intentional race.

[akpm@linux-foundation.org: reindent cpu_needs_drain, per David & Lorenzo]
Link: https://lore.kernel.org/20260626053700.2036899-1-wangxuewen@kylinos.cn
Signed-off-by: Xuewen Wang <wangxuewen@kylinos.cn>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Xuewen Wang
2026-06-26 13:37:00 +08:00
committed by Andrew Morton
parent 83fd5cbe65
commit f078b0a072
1 changed files with 7 additions and 7 deletions
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14
mm/swap.c
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@@ -831,13 +831,13 @@ static bool cpu_needs_drain(unsigned int cpu)
struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu);
/* Check these in order of likelihood that they're not zero */
return folio_batch_count(&fbatches->lru_add) ||
folio_batch_count(&fbatches->lru_move_tail) ||
folio_batch_count(&fbatches->lru_deactivate_file) ||
folio_batch_count(&fbatches->lru_deactivate) ||
folio_batch_count(&fbatches->lru_lazyfree) ||
folio_batch_count(&fbatches->lru_activate) ||
need_mlock_drain(cpu) ||
return data_race(folio_batch_count(&fbatches->lru_add) ||
folio_batch_count(&fbatches->lru_move_tail) ||
folio_batch_count(&fbatches->lru_deactivate_file) ||
folio_batch_count(&fbatches->lru_deactivate) ||
folio_batch_count(&fbatches->lru_lazyfree) ||
folio_batch_count(&fbatches->lru_activate) ||
need_mlock_drain(cpu)) ||
has_bh_in_lru(cpu, NULL);
}