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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id o129sm2142898qke.109.2020.03.06.06.16.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Mar 2020 06:16:21 -0800 (PST) Message-ID: <1583504179.7365.158.camel@lca.pw> Subject: Re: [PATCH -next] x86/mm/pat: mark an intentional data race From: Qian Cai To: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, elver@google.com, x86@kernel.org, linux-kernel@vger.kernel.org Date: Fri, 06 Mar 2020 09:16:19 -0500 In-Reply-To: <1581343816-6490-1-git-send-email-cai@lca.pw> References: <1581343816-6490-1-git-send-email-cai@lca.pw> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2020-02-10 at 09:10 -0500, Qian Cai wrote: > cpa_4k_install could be accessed concurrently as noticed by KCSAN, > > read to 0xffffffffaa59a000 of 8 bytes by interrupt on cpu 7: > cpa_inc_4k_install arch/x86/mm/pat/set_memory.c:131 [inline] > __change_page_attr+0x10cf/0x1840 arch/x86/mm/pat/set_memory.c:1514 > __change_page_attr_set_clr+0xce/0x490 arch/x86/mm/pat/set_memory.c:1636 > __set_pages_np+0xc4/0xf0 arch/x86/mm/pat/set_memory.c:2148 > __kernel_map_pages+0xb0/0xc8 arch/x86/mm/pat/set_memory.c:2178 > kernel_map_pages include/linux/mm.h:2719 [inline] > > write to 0xffffffffaa59a000 of 8 bytes by task 1 on cpu 6: > cpa_inc_4k_install arch/x86/mm/pat/set_memory.c:131 [inline] > __change_page_attr+0x10ea/0x1840 arch/x86/mm/pat/set_memory.c:1514 > __change_page_attr_set_clr+0xce/0x490 arch/x86/mm/pat/set_memory.c:1636 > __set_pages_p+0xc4/0xf0 arch/x86/mm/pat/set_memory.c:2129 > __kernel_map_pages+0x2e/0xc8 arch/x86/mm/pat/set_memory.c:2176 > kernel_map_pages include/linux/mm.h:2719 [inline] > > Both accesses are due to the same "cpa_4k_install++" in > cpa_inc_4k_install. A data race here could be potentially undesirable: > depending on compiler optimizations or how x86 executes a non-LOCK'd > increment, it may lose increments, corrupt the counter, etc. Since this > counter only seems to be used for printing some stats, this data race > itself is unlikely to cause harm to the system though. Thus, mark this > intentional data race using the data_race() marco. Borislav or any other maintainers, can you take a look at this patch when you had a chance? > > Suggested-by: Macro Elver > Signed-off-by: Qian Cai > --- > arch/x86/mm/pat/set_memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index c4aedd00c1ba..ea0b6df950ee 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -128,7 +128,7 @@ static inline void cpa_inc_2m_checked(void) > > static inline void cpa_inc_4k_install(void) > { > - cpa_4k_install++; > + data_race(cpa_4k_install++); > } > > static inline void cpa_inc_lp_sameprot(int level)