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[2a02:3100:b105:e101:a437:493a:4de9:ee3e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499542851d6sm192408105e9.12.2026.08.07.13.50.43 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 07 Aug 2026 13:50:44 -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 Subject: [PATCH 1/5] kcov: add kcov_pause()/kcov_resume() helpers Date: Fri, 7 Aug 2026 22:50:23 +0200 Message-Id: <20260807205027.31972-2-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-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Interrupt-return work can run after HARDIRQ_OFFSET is dropped, when in_task() is true. KCOV then attributes instrumented callees to the interrupted task. Add a KCOV_PAUSED bit next to KCOV_IN_CTXSW and mask both in kcov_mode_enabled(). The context switch suppression keeps its own bit: kcov_prepare_switch() runs on the previous task and kcov_finish_switch() on the one switched in, so its lifetime is not a pause section. Sections nest by passing the state returned by kcov_pause() to kcov_resume(). Both operate on current. When task KCOV is active, remote softirq sections save and restore the complete mode, preserving the pause state. The helpers are __always_inline, and the caller must be uninstrumented: inlining does not remove the caller's own coverage callbacks. Assisted-by: Claude:claude-opus-4-8 Assisted-by: Claude:claude-fable-5 Signed-off-by: Karl Mehltretter --- include/linux/kcov.h | 25 ++++++++++++++++++++++++- kernel/kcov.c | 2 +- 2 files changed, 25 insertions(+), 2 deletions(-) diff --git a/include/linux/kcov.h b/include/linux/kcov.h index 895b761b2db1..5a0a1a9bb7ef 100644 --- a/include/linux/kcov.h +++ b/include/linux/kcov.h @@ -2,6 +2,7 @@ #ifndef _LINUX_KCOV_H #define _LINUX_KCOV_H +#include #include #include @@ -23,7 +24,8 @@ enum kcov_mode { KCOV_MODE_TRACE_CMP = 3, }; -#define KCOV_IN_CTXSW (1 << 30) +#define KCOV_IN_CTXSW BIT(30) +#define KCOV_PAUSED BIT(29) void kcov_task_init(struct task_struct *t); void kcov_task_exit(struct task_struct *t); @@ -38,6 +40,25 @@ do { \ (t)->kcov_mode &= ~KCOV_IN_CTXSW; \ } while (0) +/* + * Pause coverage for current. Pass the returned state to kcov_resume(). + * Callers must be uninstrumented. + */ +static __always_inline unsigned int kcov_pause(struct task_struct *t) +{ + unsigned int paused; + + paused = t->kcov_mode & KCOV_PAUSED; + t->kcov_mode |= KCOV_PAUSED; + return paused; +} + +static __always_inline void kcov_resume(struct task_struct *t, unsigned int paused) +{ + if (!paused) + t->kcov_mode &= ~KCOV_PAUSED; +} + /* See Documentation/dev-tools/kcov.rst for usage details. */ void kcov_remote_start(u64 handle); void kcov_remote_stop(void); @@ -93,6 +114,8 @@ void __sanitizer_cov_trace_switch(kcov_u64 val, void *cases); static inline void kcov_task_init(struct task_struct *t) {} static inline void kcov_task_exit(struct task_struct *t) {} +static inline unsigned int kcov_pause(struct task_struct *t) { return 0; } +static inline void kcov_resume(struct task_struct *t, unsigned int paused) {} static inline void kcov_prepare_switch(struct task_struct *t) {} static inline void kcov_finish_switch(struct task_struct *t) {} static inline void kcov_remote_start(u64 handle) {} diff --git a/kernel/kcov.c b/kernel/kcov.c index 1df373fb562b..83d53e383822 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -830,7 +830,7 @@ static const struct file_operations kcov_fops = { static inline bool kcov_mode_enabled(unsigned int mode) { - return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED; + return (mode & ~(KCOV_IN_CTXSW | KCOV_PAUSED)) != KCOV_MODE_DISABLED; } static void kcov_remote_softirq_start(struct task_struct *t) -- 2.53.0