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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id p19sm1024733qte.81.2020.02.05.19.55.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Feb 2020 19:55:21 -0800 (PST) From: Qian Cai To: akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qian Cai Subject: [PATCH -next] mm/swap_state: mark an intentional data race Date: Wed, 5 Feb 2020 22:55:16 -0500 Message-Id: <20200206035516.2593-1-cai@lca.pw> X-Mailer: git-send-email 2.21.0 (Apple Git-122.2) MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.012920, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: swap_cache_info.find_total could be accessed concurrently as noticed by KCSAN, BUG: KCSAN: data-race in lookup_swap_cache / lookup_swap_cache write to 0xffffffff85517318 of 8 bytes by task 94138 on cpu 101: lookup_swap_cache+0x12e/0x460 lookup_swap_cache at mm/swap_state.c:322 do_swap_page+0x112/0xeb0 __handle_mm_fault+0xc7a/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 read to 0xffffffff85517318 of 8 bytes by task 91655 on cpu 100: lookup_swap_cache+0x117/0x460 lookup_swap_cache at mm/swap_state.c:322 shmem_swapin_page+0xc7/0x9e0 shmem_getpage_gfp+0x2ca/0x16c0 shmem_fault+0xef/0x3c0 __do_fault+0x9e/0x220 do_fault+0x4a0/0x920 __handle_mm_fault+0xc69/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 Reported by Kernel Concurrency Sanitizer on: CPU: 100 PID: 91655 Comm: systemd-journal Tainted: G W O L 5.5.0-next-20200204+ #6 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 Both the read and write are done as lockless. Since INC_CACHE_INFO() is only used for swap_cache_info.find_total and swap_cache_info.find_success which both are information counters, even if any of them missed a few incremental due to data races, it will be harmless, so just mark it as an intentional data race using the data_race() macro. While at it, fix a checkpatch.pl warning, WARNING: Single statement macros should not use a do {} while (0) loop Signed-off-by: Qian Cai --- mm/swap_state.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index 8e7ce9a9bc5e..b964c1391362 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -58,8 +58,8 @@ static bool enable_vma_readahead __read_mostly = true; #define GET_SWAP_RA_VAL(vma) \ (atomic_long_read(&(vma)->swap_readahead_info) ? : 4) -#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) -#define ADD_CACHE_INFO(x, nr) do { swap_cache_info.x += (nr); } while (0) +#define INC_CACHE_INFO(x) data_race(swap_cache_info.x++) +#define ADD_CACHE_INFO(x, nr) (swap_cache_info.x += (nr)) static struct { unsigned long add_total;