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b=R5WdPwK8joJmZRx7kOg1Iee7tBSPqd4RG87rlVXg2TpGSjTEz6TKvXe6YV/0x+IgE qk8vnRZPkMLuadN/8xJckx1lO0wf7RF/L4lmzgI7Nd07gu9uzdbY+YY72UqlIZMPhU KPMiWVijIhE1ReB+DUJk6XamyQceTWG7RvHEREHyLIOxhuBoBTqPggmrjWDfuj2qPD rRkOyUDj4dS/tGxSkN6BTwzxTIxbZEBATG7h/neXGyjE6qZm7Vvve6D71BQJwgo5gm rdNUf6tKSNC+bf6dZ9qRHX+sDjO6CYchzdBO1sziapvzZXDlHK4rEqVQv/UpvOLF6n EHT2CLYq27hTQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Andrew Morton , Ingo Molnar , Marcelo Tosatti , Michal Hocko , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Valentin Schneider , Vlastimil Babka , linux-mm@kvack.org Subject: [PATCH 1/6] task_work: Provide means to check if a work is queued Date: Thu, 3 Jul 2025 16:07:12 +0200 Message-ID: <20250703140717.25703-2-frederic@kernel.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250703140717.25703-1-frederic@kernel.org> References: <20250703140717.25703-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BDA9B20023 X-Stat-Signature: 7g7tedmfiny7jk9mu8o7747ygihtg8h7 X-Rspam-User: X-HE-Tag: 1751551656-164614 X-HE-Meta: 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 swxEEX8p dj6BTAUYv0K2xu7ovvwJHA+LxIe0UIh8p14Tm+8a0zUiUgd4Ouv6w60iLL99ehW4/+A36uOkjsnB0zWjHSLKdAqULMlrnt22gzyywbitdacl87noVPgQcCgB/3jTpvMPHBegmxOYMAQcu8wQO6LSeZYGXghLb7UXqCheBOmo8WtHwjnEXTqHbtLhnPedZTiaI+iE8HLWW8qfevb0/JnNZHurFSIHv4lyiz5jhw9OmxzhWo1aL+lUI/Gx7jMPqarQxyPZwYtKJibR4PTUTplFNQmtQcLZ8QzV8kEAZjFE4191a2XWZzsAcZbXTh5NGUbt5AnnkOk8nJFVFnG3RgQue0bWRW/hrjUYvFHEyjQP37ohTwpU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Some task work users implement their own ways to know if a callback is already queued on the current task while fiddling with the callback head internals. Provide instead a consolidated API to serve this very purpose. Reviewed-by: Oleg Nesterov Reviewed-by: Valentin Schneider Signed-off-by: Frederic Weisbecker --- include/linux/task_work.h | 12 ++++++++++++ kernel/task_work.c | 9 +++++++-- 2 files changed, 19 insertions(+), 2 deletions(-) diff --git a/include/linux/task_work.h b/include/linux/task_work.h index 0646804860ff..31caf12c1313 100644 --- a/include/linux/task_work.h +++ b/include/linux/task_work.h @@ -5,12 +5,15 @@ #include #include +#define TASK_WORK_DEQUEUED ((void *) -1UL) + typedef void (*task_work_func_t)(struct callback_head *); static inline void init_task_work(struct callback_head *twork, task_work_func_t func) { twork->func = func; + twork->next = TASK_WORK_DEQUEUED; } enum task_work_notify_mode { @@ -26,6 +29,15 @@ static inline bool task_work_pending(struct task_struct *task) return READ_ONCE(task->task_works); } +/* + * Check if a work is queued. Beware: this is inherently racy if the work can + * be queued elsewhere than the current task. + */ +static inline bool task_work_queued(struct callback_head *twork) +{ + return twork->next != TASK_WORK_DEQUEUED; +} + int task_work_add(struct task_struct *task, struct callback_head *twork, enum task_work_notify_mode mode); diff --git a/kernel/task_work.c b/kernel/task_work.c index d1efec571a4a..56718cb824d9 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -67,8 +67,10 @@ int task_work_add(struct task_struct *task, struct callback_head *work, head = READ_ONCE(task->task_works); do { - if (unlikely(head == &work_exited)) + if (unlikely(head == &work_exited)) { + work->next = TASK_WORK_DEQUEUED; return -ESRCH; + } work->next = head; } while (!try_cmpxchg(&task->task_works, &head, work)); @@ -129,8 +131,10 @@ task_work_cancel_match(struct task_struct *task, if (!match(work, data)) { pprev = &work->next; work = READ_ONCE(*pprev); - } else if (try_cmpxchg(pprev, &work, work->next)) + } else if (try_cmpxchg(pprev, &work, work->next)) { + work->next = TASK_WORK_DEQUEUED; break; + } } raw_spin_unlock_irqrestore(&task->pi_lock, flags); @@ -224,6 +228,7 @@ void task_work_run(void) do { next = work->next; + work->next = TASK_WORK_DEQUEUED; work->func(work); work = next; cond_resched(); -- 2.48.1