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Date: Tue, 28 Jan 2020 23:20:19 -0500 From: Qian Cai <cai@....pw> To: akpm@...ux-foundation.org Cc: hannes@...xchg.org, elver@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Qian Cai <cai@....pw> Subject: [PATCH -next] mm/page_counter: mark intentional data races The commit 3e32cb2e0a12 ("mm: memcontrol: lockless page counters") had memcg->memsw->failcnt and ->watermark could be accessed concurrently as reported by KCSAN, Reported by Kernel Concurrency Sanitizer on: BUG: KCSAN: data-race in page_counter_try_charge / page_counter_try_charge read to 0xffff8fb18c4cd190 of 8 bytes by task 1081 on cpu 59: page_counter_try_charge+0x4d/0x150 mm/page_counter.c:138 try_charge+0x131/0xd50 __memcg_kmem_charge_memcg+0x58/0x140 __memcg_kmem_charge+0xcc/0x280 __alloc_pages_nodemask+0x1e1/0x450 alloc_pages_current+0xa6/0x120 pte_alloc_one+0x17/0xd0 __pte_alloc+0x3a/0x1f0 copy_p4d_range+0xc36/0x1990 copy_page_range+0x21d/0x360 dup_mmap+0x5f5/0x7a0 dup_mm+0xa2/0x240 copy_process+0x1b3f/0x3460 _do_fork+0xaa/0xa20 __x64_sys_clone+0x13b/0x170 do_syscall_64+0x91/0xb47 entry_SYSCALL_64_after_hwframe+0x49/0xbe write to 0xffff8fb18c4cd190 of 8 bytes by task 1153 on cpu 120: page_counter_try_charge+0x5b/0x150 mm/page_counter.c:139 try_charge+0x131/0xd50 mem_cgroup_try_charge+0x159/0x460 mem_cgroup_try_charge_delay+0x3d/0xa0 wp_page_copy+0x14d/0x930 do_wp_page+0x107/0x7b0 __handle_mm_fault+0xce6/0xd40 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 Since the failcnt and watermark are tolerant of some inaccuracy, a data race will not be harmful, thus mark them as intentional data races with the data_race() macro. Signed-off-by: Qian Cai <cai@....pw> --- mm/page_counter.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/mm/page_counter.c b/mm/page_counter.c index de31470655f6..13934636eafd 100644 --- a/mm/page_counter.c +++ b/mm/page_counter.c @@ -82,8 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages) * This is indeed racy, but we can live with some * inaccuracy in the watermark. */ - if (new > c->watermark) - c->watermark = new; + if (data_race(new > c->watermark)) + data_race(c->watermark = new); } } @@ -126,7 +126,7 @@ bool page_counter_try_charge(struct page_counter *counter, * This is racy, but we can live with some * inaccuracy in the failcnt. */ - c->failcnt++; + data_race(c->failcnt++); *fail = c; goto failed; } @@ -135,8 +135,8 @@ bool page_counter_try_charge(struct page_counter *counter, * Just like with failcnt, we can live with some * inaccuracy in the watermark. */ - if (new > c->watermark) - c->watermark = new; + if (data_race(new > c->watermark)) + data_race(c->watermark = new); } return true; -- 2.21.0 (Apple Git-122.2)
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