[RFC PATCH v2 10/13] mm/kwatch: add anchor thread for global watchpoints
From: Jinchao Wang <hidden>
Date: 2026-07-17 13:06:30
Also in:
linux-doc, linux-perf-users, lkml
Subsystem:
memory management, the rest · Maintainers:
Andrew Morton, Linus Torvalds
Global variables have no function whose execution can bound the watch window. Provide one: a kernel thread sleeps for the configured duration inside a dedicated noinline function, kwatch_global_anchor(), and the probe runtime hooks that function like any other target. When the duration expires the thread schedules a work item that tears the session down; the expired flag is cleared under the control-plane mutex so a stale work item from a previous session cannot stop a new one. Signed-off-by: Jinchao Wang <redacted> --- mm/kwatch/Makefile | 2 +- mm/kwatch/anchor.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 86 insertions(+), 1 deletion(-) create mode 100644 mm/kwatch/anchor.c
diff --git a/mm/kwatch/Makefile b/mm/kwatch/Makefile
index f04673cc5b1c..b196c794619a 100644
--- a/mm/kwatch/Makefile
+++ b/mm/kwatch/Makefile@@ -1,3 +1,3 @@ obj-$(CONFIG_KWATCH) += kwatch.o -kwatch-y := deref.o task_ctx.o hwbp.o probe.o +kwatch-y := deref.o task_ctx.o hwbp.o probe.o anchor.o
diff --git a/mm/kwatch/anchor.c b/mm/kwatch/anchor.c
new file mode 100644
index 000000000000..e87eb5e813ff
--- /dev/null
+++ b/mm/kwatch/anchor.c@@ -0,0 +1,85 @@ +// SPDX-License-Identifier: GPL-2.0 +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include <linux/kthread.h> +#include <linux/wait.h> +#include <linux/jiffies.h> +#include <linux/err.h> +#include <linux/workqueue.h> + +#include "kwatch.h" + +static DECLARE_WAIT_QUEUE_HEAD(kwatch_anchor_wq); +static struct task_struct *kwatch_anchor_tsk; +static bool kwatch_anchor_expired; + +bool kwatch_anchor_has_expired(void) +{ + return READ_ONCE(kwatch_anchor_expired); +} + +void kwatch_anchor_clear_expired(void) +{ + WRITE_ONCE(kwatch_anchor_expired, false); +} + +static void kwatch_auto_stop_handler(struct work_struct *work) +{ + kwatch_auto_stop(); +} + +static DECLARE_WORK(kwatch_auto_stop_work, kwatch_auto_stop_handler); + +noinline void kwatch_global_anchor(unsigned long duration_sec) +{ + /* TASK_IDLE: a long timed sleep must not inflate loadavg or trip the + * hung-task detector the way TASK_UNINTERRUPTIBLE would. + */ + wait_event_idle_timeout(kwatch_anchor_wq, kthread_should_stop(), + duration_sec * HZ); +} + +static int kwatch_anchor_thread_fn(void *data) +{ + unsigned long duration = (unsigned long)data; + + kwatch_global_anchor(duration); + + if (!kthread_should_stop()) { + /* mark before scheduling; cleared under the control mutex */ + WRITE_ONCE(kwatch_anchor_expired, true); + schedule_work(&kwatch_auto_stop_work); + } + + while (!kthread_should_stop()) + schedule_timeout_idle(HZ); + + return 0; +} + +int kwatch_anchor_start(u16 duration) +{ + kwatch_anchor_tsk = kthread_run(kwatch_anchor_thread_fn, + (void *)(unsigned long)duration, + "kwatch_anchor"); + if (IS_ERR(kwatch_anchor_tsk)) { + int ret = PTR_ERR(kwatch_anchor_tsk); + + kwatch_anchor_tsk = NULL; + return ret; + } + return 0; +} + +void kwatch_anchor_stop(void) +{ + if (kwatch_anchor_tsk) { + kthread_stop(kwatch_anchor_tsk); + kwatch_anchor_tsk = NULL; + } +} + +void kwatch_anchor_cancel_work(void) +{ + cancel_work_sync(&kwatch_auto_stop_work); +}
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2.53.0