From: "Paul E. McKenney" <paulmck@kernel.org>
To: linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
kernel-team@fb.com, mingo@kernel.org
Cc: elver@google.com, andreyknvl@google.com, glider@google.com,
dvyukov@google.com, cai@lca.pw, boqun.feng@gmail.com
Subject: Re: [PATCH kcsan 27/32] kcsan: Add option to allow watcher interruptions
Date: Thu, 12 Mar 2020 11:04:14 -0700 [thread overview]
Message-ID: <20200312180414.GA8024@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200312180328.GA4772@paulmck-ThinkPad-P72>
On Thu, Mar 12, 2020 at 11:03:28AM -0700, Paul E. McKenney wrote:
> On Mon, Mar 09, 2020 at 12:04:15PM -0700, paulmck@kernel.org wrote:
> > From: Marco Elver <elver@google.com>
> >
> > Add option to allow interrupts while a watchpoint is set up. This can be
> > enabled either via CONFIG_KCSAN_INTERRUPT_WATCHER or via the boot
> > parameter 'kcsan.interrupt_watcher=1'.
> >
> > Note that, currently not all safe per-CPU access primitives and patterns
> > are accounted for, which could result in false positives. For example,
> > asm-generic/percpu.h uses plain operations, which by default are
> > instrumented. On interrupts and subsequent accesses to the same
> > variable, KCSAN would currently report a data race with this option.
> >
> > Therefore, this option should currently remain disabled by default, but
> > may be enabled for specific test scenarios.
> >
> > To avoid new warnings, changes all uses of smp_processor_id() to use the
> > raw version (as already done in kcsan_found_watchpoint()). The exact SMP
> > processor id is for informational purposes in the report, and
> > correctness is not affected.
> >
> > Signed-off-by: Marco Elver <elver@google.com>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
> And I get silent hangs that bisect to this patch when running the
> following rcutorture command, run in the kernel source tree on a
> 12-hardware-thread laptop:
>
> bash tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 12 --duration 10 --kconfig "CONFIG_DEBUG_INFO=y CONFIG_KCSAN=y CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000 CONFIG_KCSAN_VERBOSE=y CONFIG_KCSAN_INTERRUPT_WATCHER=y" --configs TREE03
>
> It works fine on some (but not all) of the other rcutorture test
> scenarios. It fails on TREE01, TREE02, TREE03, TREE09. The common thread
> is that these are the TREE scenarios are all PREEMPT=y. So are RUDE01,
> SRCU-P, TASKS01, and TASKS03, but these scenarios are not hammering
> on Tree RCU, and thus have far less interrupt activity and the like.
> Given that it is an interrupt-related feature being added by this commit,
> this seems like expected (mis)behavior.
>
> Can you reproduce this? If not, are there any diagnostics I can add to
> my testing? Or a diagnostic patch I could apply?
I should hasten to add that this feature was quite helpful in recent work!
Thanx, Paul
next prev parent reply other threads:[~2020-03-12 18:04 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-09 19:03 [PATCH kcsan 0/32] KCSAN commits for v5.7 Paul E. McKenney
2020-03-09 19:03 ` [PATCH kcsan 01/32] kcsan: Prefer __always_inline for fast-path paulmck
2020-03-09 19:03 ` [PATCH kcsan 02/32] kcsan: Show full access type in report paulmck
2020-03-09 19:03 ` [PATCH kcsan 03/32] kcsan: Rate-limit reporting per data races paulmck
2020-03-09 19:03 ` [PATCH kcsan 04/32] kcsan: Make KCSAN compatible with lockdep paulmck
2020-03-09 19:03 ` [PATCH kcsan 05/32] kcsan: Address missing case with KCSAN_REPORT_VALUE_CHANGE_ONLY paulmck
2020-03-09 19:03 ` [PATCH kcsan 06/32] include/linux: Add instrumented.h infrastructure paulmck
2020-03-09 19:03 ` [PATCH kcsan 07/32] asm-generic, atomic-instrumented: Use generic instrumented.h paulmck
2020-03-09 19:03 ` [PATCH kcsan 08/32] asm-generic, kcsan: Add KCSAN instrumentation for bitops paulmck
2020-03-09 19:03 ` [PATCH kcsan 09/32] iov_iter: Use generic instrumented.h paulmck
2020-03-09 19:03 ` [PATCH kcsan 10/32] copy_to_user, copy_from_user: " paulmck
2020-03-09 19:03 ` [PATCH kcsan 11/32] kcsan: Add docbook header for data_race() paulmck
2020-03-09 19:04 ` [PATCH kcsan 12/32] kcsan: Add option to assume plain aligned writes up to word size are atomic paulmck
2020-03-09 19:04 ` [PATCH kcsan 13/32] kcsan: Clarify Kconfig option KCSAN_IGNORE_ATOMICS paulmck
2020-03-09 19:04 ` [PATCH kcsan 14/32] kcsan: Cleanup of main KCSAN Kconfig option paulmck
2020-03-09 19:04 ` [PATCH kcsan 15/32] kcsan: Fix 0-sized checks paulmck
2020-03-09 19:04 ` [PATCH kcsan 16/32] kcsan: Introduce KCSAN_ACCESS_ASSERT access type paulmck
2020-03-09 19:04 ` [PATCH kcsan 17/32] kcsan: Introduce ASSERT_EXCLUSIVE_* macros paulmck
2020-03-13 8:52 ` Boqun Feng
2020-03-13 16:15 ` Marco Elver
2020-03-14 2:22 ` Boqun Feng
2020-03-17 11:12 ` Marco Elver
2020-03-19 3:23 ` Boqun Feng
2020-03-20 14:49 ` Marco Elver
2020-03-09 19:04 ` [PATCH kcsan 18/32] kcsan: Add test to generate conflicts via debugfs paulmck
2020-03-09 19:04 ` [PATCH kcsan 19/32] kcsan: Expose core configuration parameters as module params paulmck
2020-03-09 19:04 ` [PATCH kcsan 20/32] kcsan: Fix misreporting if concurrent races on same address paulmck
2020-03-09 19:04 ` [PATCH kcsan 21/32] kcsan: Move interfaces that affects checks to kcsan-checks.h paulmck
2020-03-09 19:04 ` [PATCH kcsan 22/32] compiler.h, seqlock.h: Remove unnecessary kcsan.h includes paulmck
2020-03-09 19:04 ` [PATCH kcsan 23/32] kcsan: Introduce kcsan_value_change type paulmck
2020-03-09 19:04 ` [PATCH kcsan 24/32] kcsan: Add kcsan_set_access_mask() support paulmck
2020-03-09 19:04 ` [PATCH kcsan 25/32] kcsan: Introduce ASSERT_EXCLUSIVE_BITS(var, mask) paulmck
2020-03-09 19:04 ` [PATCH kcsan 26/32] kcsan, trace: Make KCSAN compatible with tracing paulmck
2020-03-09 19:57 ` Steven Rostedt
2020-03-09 20:27 ` Paul E. McKenney
2020-03-09 19:04 ` [PATCH kcsan 27/32] kcsan: Add option to allow watcher interruptions paulmck
2020-03-12 18:03 ` Paul E. McKenney
2020-03-12 18:04 ` Paul E. McKenney [this message]
2020-03-13 15:28 ` Marco Elver
2020-03-16 13:56 ` Marco Elver
2020-03-16 15:45 ` Paul E. McKenney
2020-03-16 16:22 ` Marco Elver
2020-03-17 17:13 ` Paul E. McKenney
2020-03-17 17:44 ` Marco Elver
2020-03-18 17:42 ` Marco Elver
2020-03-09 19:04 ` [PATCH kcsan 28/32] kcsan: Add option for verbose reporting paulmck
2020-03-09 19:04 ` [PATCH kcsan 29/32] kcsan: Add current->state to implicitly atomic accesses paulmck
2020-03-09 19:04 ` [PATCH kcsan 30/32] kcsan: Fix a typo in a comment paulmck
2020-03-09 19:04 ` [PATCH kcsan 31/32] kcsan: Update Documentation/dev-tools/kcsan.rst paulmck
2020-03-09 19:04 ` [PATCH kcsan 32/32] kcsan: Update API documentation in kcsan-checks.h paulmck
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