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[2a02:3100:a133:e401:bc8e:d36c:2d08:c5e0]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4997aaa7aabsm1670275e9.7.2026.08.11.08.41.30 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 11 Aug 2026 08:41:31 -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 v2 5/6] sched/core: Pause KCOV in try_to_wake_up() Date: Tue, 11 Aug 2026 17:41:10 +0200 Message-Id: <20260811154111.64669-6-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260811154111.64669-1-kmehltretter@gmail.com> References: <20260811154111.64669-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit try_to_wake_up() is uninstrumented, but it calls instrumented helpers 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. Wrapping only select_task_rq() would miss SCHED_HRTICK arming during enqueue. Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") Assisted-by: Claude:claude-fable-5 Signed-off-by: Karl Mehltretter --- Notes: v2: - take guard(kcov_pause)() - describe the paused wakeup body precisely kernel/sched/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e49f0bfa0ca73..e863fac02e38f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4253,6 +4253,9 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) guard(preempt)(); int cpu, success = 0; + /* Instrumented callees would leak coverage into current. */ + guard(kcov_pause)(); + wake_flags |= WF_TTWU; if (p == current) { -- 2.53.0