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[2a02:3100:b105:e101:a437:493a:4de9:ee3e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499542851d6sm192408105e9.12.2026.08.07.13.50.50 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 07 Aug 2026 13:50:51 -0700 (PDT) From: Karl Mehltretter To: Andrew Morton Cc: Karl Mehltretter , Andrey Konovalov , Dmitry Vyukov , Alexander Potapenko , Marco Elver , Bradley Morgan , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Juri Lelli , Vincent Guittot , Steven Rostedt , Sebastian Andrzej Siewior , Clark Williams , linux-rt-devel@lists.linux.dev Subject: [PATCH 4/5] sched: pause KCOV in try_to_wake_up() Date: Fri, 7 Aug 2026 22:50:26 +0200 Message-Id: <20260807205027.31972-5-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260807205027.31972-1-kmehltretter@gmail.com> References: <20260807205027.31972-1-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 all of try_to_wake_up(). Wrapping only select_task_rq() would miss SCHED_HRTICK arming during enqueue. Fixes: 5c9a8750a640 ("kernel: add kcov code coverage") Assisted-by: Claude:claude-opus-4-8 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 d5663df6c702..1e562a7ff0af 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4252,6 +4252,8 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) { guard(preempt)(); int cpu, success = 0; + /* KCOV: sched/ is uninstrumented but the wakeup callees are not. */ + unsigned int kcov_paused = kcov_pause(current); wake_flags |= WF_TTWU; @@ -4418,6 +4420,7 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) if (success) ttwu_stat(p, task_cpu(p), wake_flags); + kcov_resume(current, kcov_paused); return success; } -- 2.53.0