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[2a02:3100:b305:2001:39fa:3d24:821a:4eae]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a0394e6c5asm281196795e9.2.2026.10.05.11.58.24 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 05 Oct 2026 11:58:25 -0700 (PDT) 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 v4 4/6] sched/core: Pause KCOV in __schedule() Date: Mon, 5 Oct 2026 20:58:01 +0200 Message-Id: <20261005185803.39170-5-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20261005185803.39170-1-kmehltretter@gmail.com> References: <20261005185803.39170-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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. Assisted-by: LLM 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 87cff2884980..419dd98645bd 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7123,6 +7123,9 @@ static void __sched notrace __schedule(int sched_mode) struct rq *rq; int cpu; + /* Callees instrumented with KCOV would leak coverage into current. */ + guard(kcov_pause)(); + /* Trace preemptions consistently with task switches */ trace_sched_entry_tp(sched_mode == SM_PREEMPT); -- 2.53.0