[PATCH v3 08/19] mm/ksw: support CPU hotplug

Jinchao Wang
2025-09-10T05:26:08Z

Register CPU online/offline callbacks via cpuhp_setup_state_nocalls()
so stack watches are installed/removed dynamically as CPUs come online
or go offline.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
mm/kstackwatch/watch.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/mm/kstackwatch/watch.c b/mm/kstackwatch/watch.c
index e02ffc3231ad..d95efefdffe9 100644
--- a/mm/kstackwatch/watch.c
+++ b/mm/kstackwatch/watch.c
@@ -1,6 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/cpuhotplug.h>
#include <linux/hw_breakpoint.h>
#include <linux/perf_event.h>
#include <linux/preempt.h>
@@ -67,6 +68,32 @@ static void ksw_watch_on_local_cpu(void *data)
}
}

+static int ksw_cpu_online(unsigned int cpu)
+{
+ struct perf_event *bp;
+
+ bp = perf_event_create_kernel_counter(&watch_attr, cpu, NULL,
+ ksw_watch_handler, NULL);
+ if (IS_ERR(bp)) {
+ pr_err("Failed to create watch on CPU %d: %ld\n", cpu,
+ PTR_ERR(bp));
+ return PTR_ERR(bp);
+ }
+
+ per_cpu(*watch_events, cpu) = bp;
+ per_cpu(watch_csd, cpu) = CSD_INIT(ksw_watch_on_local_cpu, NULL);
+ return 0;
+}
+
+static int ksw_cpu_offline(unsigned int cpu)
+{
+ struct perf_event *bp = per_cpu(*watch_events, cpu);
+
+ if (bp)
+ unregister_hw_breakpoint(bp);
+ return 0;
+}
+
int ksw_watch_on(u64 watch_addr, u64 watch_len)
{
unsigned long flags;
@@ -141,6 +168,15 @@ int ksw_watch_init(void)
return ret;
}

+ ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+ "kstackwatch:online", ksw_cpu_online,
+ ksw_cpu_offline);
+ if (ret < 0) {
+ unregister_wide_hw_breakpoint(watch_events);
+ pr_err("Failed to register CPU hotplug notifier\n");
+ return ret;
+ }
+
return 0;
}

--
2.43.0