From: 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,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH kcsan 20/32] kcsan: Fix misreporting if concurrent races on same address
Date: Mon, 9 Mar 2020 12:04:08 -0700 [thread overview]
Message-ID: <20200309190420.6100-20-paulmck@kernel.org> (raw)
In-Reply-To: <20200309190359.GA5822@paulmck-ThinkPad-P72>
From: Marco Elver <elver@google.com>
If there are at least 4 threads racing on the same address, it can
happen that one of the readers may observe another matching reader in
other_info. To avoid locking up, we have to consume 'other_info'
regardless, but skip the report. See the added comment for more details.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/kcsan/report.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 3bc590e..abf6852 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -422,6 +422,44 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
return false;
}
+ access_type |= other_info.access_type;
+ if ((access_type & KCSAN_ACCESS_WRITE) == 0) {
+ /*
+ * While the address matches, this is not the other_info
+ * from the thread that consumed our watchpoint, since
+ * neither this nor the access in other_info is a write.
+ * It is invalid to continue with the report, since we
+ * only have information about reads.
+ *
+ * This can happen due to concurrent races on the same
+ * address, with at least 4 threads. To avoid locking up
+ * other_info and all other threads, we have to consume
+ * it regardless.
+ *
+ * A concrete case to illustrate why we might lock up if
+ * we do not consume other_info:
+ *
+ * We have 4 threads, all accessing the same address
+ * (or matching address ranges). Assume the following
+ * watcher and watchpoint consumer pairs:
+ * write1-read1, read2-write2. The first to populate
+ * other_info is write2, however, write1 consumes it,
+ * resulting in a report of write1-write2. This report
+ * is valid, however, now read1 populates other_info;
+ * read2-read1 is an invalid conflict, yet, no other
+ * conflicting access is left. Therefore, we must
+ * consume read1's other_info.
+ *
+ * Since this case is assumed to be rare, it is
+ * reasonable to omit this report: one of the other
+ * reports includes information about the same shared
+ * data, and at this point the likelihood that we
+ * re-report the same race again is high.
+ */
+ release_report(flags, KCSAN_REPORT_RACE_SIGNAL);
+ return false;
+ }
+
/*
* Matching & usable access in other_info: keep other_info_lock
* locked, as this thread consumes it to print the full report;
--
2.9.5
next prev parent reply other threads:[~2020-03-09 19:05 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 ` paulmck [this message]
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
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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