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[2a02:3100:b149:1401:90c6:65b4:35d:1e3d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b7e3279f9csm65132675e9.8.2026.11.07.05.17.31 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 07 Nov 2026 05:17:32 -0800 (PST) From: Karl Mehltretter To: Andrew Morton Cc: Karl Mehltretter , Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , Marco Elver , Bradley Morgan , Anna-Maria Behnsen , Frederic Weisbecker , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Sebastian Andrzej Siewior , Clark Williams , linux-rt-devel@lists.linux.dev, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org Subject: [PATCH v5 4/6] sched/core: Pause KCOV in __schedule() Date: Sat, 7 Nov 2026 14:17:08 +0100 Message-Id: <20261107131710.89264-5-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20261107131710.89264-1-kmehltretter@gmail.com> References: <20261107131710.89264-1-kmehltretter@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit kernel/sched/ is built without KCOV instrumentation, but it calls code that is instrumented with KCOV, such as sched_clock(), architecture CPU-capacity helpers and profile_hits(). During preemption and schedule() calls, these callees can add nondeterministic scheduler coverage to current. With CONFIG_KCOV_SELFTEST added to x86_64 defconfig, the interrupt selftest fails under QEMU, detecting spurious coverage in arch_scale_cpu_capacity(). Annotating each callee would spread exclusions across architectures. Pause across __schedule() instead, extending the scheduler exclusion to its callees. KCOV_PAUSED remains set while a task is switched out. The guard in its resumed __schedule() frame restores the prior state. Signed-off-by: Karl Mehltretter --- kernel/sched/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3f13170c2939..1691eb19f31a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7219,6 +7219,9 @@ static void __sched notrace __schedule(int sched_mode) struct rq *rq; int cpu; + /* Callees instrumented with KCOV would leak coverage into current. */ + kcov_pause_scope(); + /* Trace preemptions consistently with task switches */ trace_sched_entry_tp(sched_mode == SM_PREEMPT); -- 2.39.5