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Message-ID: <20240625135244.20227-2-frederic@kernel.org>
Date: Tue, 25 Jun 2024 15:52:39 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
Marcelo Tosatti <mtosatti@...hat.com>,
Vlastimil Babka <vbabka@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Oleg Nesterov <oleg@...hat.com>
Subject: [RFC PATCH 1/6] task_work: Provide means to check if a work is queued
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.
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
include/linux/task_work.h | 12 ++++++++++++
kernel/task_work.c | 1 +
2 files changed, 13 insertions(+)
diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index 795ef5a68429..f2eae971b73a 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -5,12 +5,15 @@
#include <linux/list.h>
#include <linux/sched.h>
+#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 {
@@ -25,6 +28,15 @@ 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 95a7e1b7f1da..6e3bee0b7011 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -177,6 +177,7 @@ void task_work_run(void)
do {
next = work->next;
+ work->next = TASK_WORK_DEQUEUED;
work->func(work);
work = next;
cond_resched();
--
2.45.2
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