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[2a02:3100:b305:2001:39fa:3d24:821a:4eae]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a0394e6c5asm281196795e9.2.2026.10.05.11.58.27 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 05 Oct 2026 11:58:29 -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 5/6] sched/core: Pause KCOV in try_to_wake_up() Date: Mon, 5 Oct 2026 20:58:02 +0200 Message-Id: <20261005185803.39170-6-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 try_to_wake_up() is built without KCOV instrumentation, but it calls helpers instrumented with KCOV, such as kthread_is_per_cpu(), CPU capacity helpers and SCHED_HRTICK arming. They can record into current while in_task() is true. CONFIG_KCOV_SELFTEST exposes this under PREEMPT_RT. The interrupt selftest fails on x86_64 in kthread_is_per_cpu(): RT runs the timer softirq in a thread, so the wakeup runs in task context during the selftest's spin. The same helpers leak into non-RT syscall wakeups such as a pipe write waking a reader. Pause the wakeup body with the kcov_pause guard. Take it before the preemption guard so preemption is re-enabled while KCOV remains paused. Wrapping only select_task_rq() would miss SCHED_HRTICK arming during enqueue. Assisted-by: LLM Signed-off-by: Karl Mehltretter --- kernel/sched/core.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 419dd98645bd..f19221282278 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4273,6 +4273,8 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) */ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) { + /* Callees instrumented with KCOV would leak coverage into current. */ + guard(kcov_pause)(); guard(preempt)(); int cpu, success = 0; -- 2.53.0