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Tue, 22 Oct 2019 15:49:06 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.44]) by smtp.corp.redhat.com (Postfix) with SMTP id 88EE560C57; Tue, 22 Oct 2019 15:48:59 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 22 Oct 2019 17:49:06 +0200 (CEST) Date: Tue, 22 Oct 2019 17:48:58 +0200 From: Oleg Nesterov To: Marco Elver Cc: akiyks@gmail.com, stern@rowland.harvard.edu, glider@google.com, parri.andrea@gmail.com, andreyknvl@google.com, luto@kernel.org, ard.biesheuvel@linaro.org, arnd@arndb.de, boqun.feng@gmail.com, bp@alien8.de, dja@axtens.net, dlustig@nvidia.com, dave.hansen@linux.intel.com, dhowells@redhat.com, dvyukov@google.com, hpa@zytor.com, mingo@redhat.com, j.alglave@ucl.ac.uk, joel@joelfernandes.org, corbet@lwn.net, jpoimboe@redhat.com, luc.maranget@inria.fr, mark.rutland@arm.com, npiggin@gmail.com, paulmck@linux.ibm.com, peterz@infradead.org, tglx@linutronix.de, will@kernel.org, kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-efi@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure Message-ID: <20191022154858.GA13700@redhat.com> References: <20191017141305.146193-1-elver@google.com> <20191017141305.146193-2-elver@google.com> MIME-Version: 1.0 In-Reply-To: <20191017141305.146193-2-elver@google.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: pP--3crAMhSTJdyaJUkLUQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 10/17, Marco Elver wrote: > > +=09/* > +=09 * Delay this thread, to increase probability of observing a racy > +=09 * conflicting access. > +=09 */ > +=09udelay(get_delay()); > + > +=09/* > +=09 * Re-read value, and check if it is as expected; if not, we infer a > +=09 * racy access. > +=09 */ > +=09switch (size) { > +=09case 1: > +=09=09is_expected =3D expect_value._1 =3D=3D READ_ONCE(*(const u8 *)ptr)= ; > +=09=09break; > +=09case 2: > +=09=09is_expected =3D expect_value._2 =3D=3D READ_ONCE(*(const u16 *)ptr= ); > +=09=09break; > +=09case 4: > +=09=09is_expected =3D expect_value._4 =3D=3D READ_ONCE(*(const u32 *)ptr= ); > +=09=09break; > +=09case 8: > +=09=09is_expected =3D expect_value._8 =3D=3D READ_ONCE(*(const u64 *)ptr= ); > +=09=09break; > +=09default: > +=09=09break; /* ignore; we do not diff the values */ > +=09} > + > +=09/* Check if this access raced with another. */ > +=09if (!remove_watchpoint(watchpoint)) { > +=09=09/* > +=09=09 * No need to increment 'race' counter, as the racing thread > +=09=09 * already did. > +=09=09 */ > +=09=09kcsan_report(ptr, size, is_write, smp_processor_id(), > +=09=09=09 kcsan_report_race_setup); > +=09} else if (!is_expected) { > +=09=09/* Inferring a race, since the value should not have changed. */ > +=09=09kcsan_counter_inc(kcsan_counter_races_unknown_origin); > +#ifdef CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN > +=09=09kcsan_report(ptr, size, is_write, smp_processor_id(), > +=09=09=09 kcsan_report_race_unknown_origin); > +#endif > +=09} Not sure I understand this code... Just for example. Suppose that task->state =3D TASK_UNINTERRUPTIBLE, this t= ask does __set_current_state(TASK_RUNNING), another CPU does wake_up_process(ta= sk) which does the same UNINTERRUPTIBLE -> RUNNING transition. Looks like, this is the "data race" according to kcsan? Hmm. even the "if (!(p->state & state))" check in try_to_wake_up() can trig= ger kcsan_report() ? Oleg.