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

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Message-ID: <20250910052335.1151048-9-wangjinchao600@gmail.com>
Date: Wed, 10 Sep 2025 13:23:17 +0800
From: Jinchao Wang <wangjinchao600@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Rapoport <rppt@...nel.org>,
	"Naveen N . Rao" <naveen@...nel.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	kasan-dev@...glegroups.com,
	"David S. Miller" <davem@...emloft.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-mm@...ck.org,
	linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Jinchao Wang <wangjinchao600@...il.com>
Subject: [PATCH v3 08/19] mm/ksw: support CPU hotplug

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@...il.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