From: Oleg Nesterov <oleg@redhat.com>
To: Marco Elver <elver@google.com>
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
Date: Tue, 22 Oct 2019 17:48:58 +0200 [thread overview]
Message-ID: <20191022154858.GA13700@redhat.com> (raw)
In-Reply-To: <20191017141305.146193-2-elver@google.com>
On 10/17, Marco Elver wrote:
>
> + /*
> + * Delay this thread, to increase probability of observing a racy
> + * conflicting access.
> + */
> + udelay(get_delay());
> +
> + /*
> + * Re-read value, and check if it is as expected; if not, we infer a
> + * racy access.
> + */
> + switch (size) {
> + case 1:
> + is_expected = expect_value._1 == READ_ONCE(*(const u8 *)ptr);
> + break;
> + case 2:
> + is_expected = expect_value._2 == READ_ONCE(*(const u16 *)ptr);
> + break;
> + case 4:
> + is_expected = expect_value._4 == READ_ONCE(*(const u32 *)ptr);
> + break;
> + case 8:
> + is_expected = expect_value._8 == READ_ONCE(*(const u64 *)ptr);
> + break;
> + default:
> + break; /* ignore; we do not diff the values */
> + }
> +
> + /* Check if this access raced with another. */
> + if (!remove_watchpoint(watchpoint)) {
> + /*
> + * No need to increment 'race' counter, as the racing thread
> + * already did.
> + */
> + kcsan_report(ptr, size, is_write, smp_processor_id(),
> + kcsan_report_race_setup);
> + } else if (!is_expected) {
> + /* Inferring a race, since the value should not have changed. */
> + kcsan_counter_inc(kcsan_counter_races_unknown_origin);
> +#ifdef CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
> + kcsan_report(ptr, size, is_write, smp_processor_id(),
> + kcsan_report_race_unknown_origin);
> +#endif
> + }
Not sure I understand this code...
Just for example. Suppose that task->state = TASK_UNINTERRUPTIBLE, this task
does __set_current_state(TASK_RUNNING), another CPU does wake_up_process(task)
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 trigger
kcsan_report() ?
Oleg.
next prev parent reply other threads:[~2019-10-22 15:49 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-17 14:12 [PATCH v2 0/8] Add Kernel Concurrency Sanitizer (KCSAN) Marco Elver
2019-10-17 14:12 ` [PATCH v2 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure Marco Elver
2019-10-21 13:37 ` Alexander Potapenko
2019-10-21 15:54 ` Marco Elver
2019-10-22 14:11 ` Mark Rutland
2019-10-22 16:52 ` Marco Elver
2019-10-22 15:48 ` Oleg Nesterov [this message]
2019-10-22 17:42 ` Marco Elver
2019-10-23 16:24 ` Oleg Nesterov
2019-10-24 11:02 ` Marco Elver
2019-10-23 9:41 ` Dmitry Vyukov
2019-10-23 9:56 ` Dmitry Vyukov
2019-10-23 10:03 ` Dmitry Vyukov
2019-10-23 10:09 ` Dmitry Vyukov
2019-10-23 10:28 ` Dmitry Vyukov
2019-10-23 11:08 ` Dmitry Vyukov
2019-10-23 11:20 ` Dmitry Vyukov
2019-10-23 12:05 ` Dmitry Vyukov
2019-10-23 12:32 ` Dmitry Vyukov
2019-10-17 14:12 ` [PATCH v2 2/8] objtool, kcsan: Add KCSAN runtime functions to whitelist Marco Elver
2019-10-21 15:15 ` Dmitry Vyukov
2019-10-21 15:43 ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 3/8] build, kcsan: Add KCSAN build exceptions Marco Elver
2019-10-17 14:13 ` [PATCH v2 4/8] seqlock, kcsan: Add annotations for KCSAN Marco Elver
2019-10-24 12:28 ` Mark Rutland
2019-10-24 14:17 ` Marco Elver
2019-10-24 16:35 ` Mark Rutland
2019-10-24 17:09 ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 5/8] seqlock: Require WRITE_ONCE surrounding raw_seqcount_barrier Marco Elver
2019-10-17 14:13 ` [PATCH v2 6/8] asm-generic, kcsan: Add KCSAN instrumentation for bitops Marco Elver
2019-10-17 14:13 ` [PATCH v2 7/8] locking/atomics, kcsan: Add KCSAN instrumentation Marco Elver
2019-10-22 12:33 ` Mark Rutland
2019-10-22 18:17 ` Marco Elver
2019-10-17 14:13 ` [PATCH v2 8/8] x86, kcsan: Enable KCSAN for x86 Marco Elver
2019-10-22 12:59 ` Mark Rutland
2019-10-22 13:02 ` Marco Elver
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