From nobody Sat Feb 7 08:02:39 2026 Received: from mail-dl1-f52.google.com (mail-dl1-f52.google.com [74.125.82.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5D7D5265CC2 for ; Wed, 28 Jan 2026 06:06:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.52 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769580392; cv=none; b=Ypbp758As5mVpA2EjyHtRnfns+AHQLolcW14GlMHs76xNM8uSOWKpVlEO7w99UI0oSf4SoDt7CDGhrzUUDgyL5Vzu+nR6e+zOrqcvHuhnZB3Z1xldnvWJ0fEPSGuLP0gQeKEt57pJqQxBqYdB0Usoh0nVFUoI0FIyX6yv2SsyQs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769580392; c=relaxed/simple; bh=fD/kgZvAJFHYzXjUwTyBXUwZSjmzmlfRjg/zztY3NpI=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=eB/ae4TIIvcQY8fATZIrWx+TPW6A8K39RjlNLNJX/aKPF3n3LKgnz6RR8qq3YNvP/aScZs/Elr3D0K/BwcTh4yfwP3lBx6FRBWp1KzR0CTmxYrrktC69hr19MOX3K5FFOWlO5LrzkL7bsIW5JDe4a18uo5AAruM/duabuZWNGKI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=b2BLG0eA; arc=none smtp.client-ip=74.125.82.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="b2BLG0eA" Received: by mail-dl1-f52.google.com with SMTP id a92af1059eb24-1233bc1117fso396304c88.0 for ; Tue, 27 Jan 2026 22:06:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1769580389; x=1770185189; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=ylSEp4a0zfiE/n3fKLMKe4thGKMdljP/4PNULWhpuIc=; b=b2BLG0eAbFraMpVUSm2yzawP1t1+u3Q/b3njS7jDr5in4sq5gv8K7G+incDL0jLatf 5O8SWeLqKGL/aW6D200w7ANj5aHLroKaG9s0Roo4iCH2amAZpQ4OE6YL/K1asLJqburc Fd96I1zaYEFJDj++K2XZp++Y+YIeagQ/Hn4xkn6e8alzBAPoOVW4Rawrb6Uc/+Af6yxf elckJZL0MNAdfjIS5RK07STdp+ba/lquAzT4XDkeGj4hyjiul3z6mvspfPNzjyomAksP bW3AchyQqENm60cpB1e1Ie3yK99ybITmFQnCPMe7npxfNVPB50hZbvFYJMWIRBGDfAZ6 yvqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769580389; x=1770185189; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=ylSEp4a0zfiE/n3fKLMKe4thGKMdljP/4PNULWhpuIc=; b=T0hh5yODs1BAhU9wje1KD8tRWz84/7aUt+BnsJfxSQspNEDI1HiVUiqzkfcfwvHvRT RBAXxRr0zjnTEUJuCrtEXD/Grty+oZJNqPRqbRfwXlK2M1OyU8nbVTQgYqSKiXAEFB1u U87a/+4VbegXObJJaxpEkqr4TGoY9al7UwQge6Gr94nU97L2WtPRoPuFN1oOCr25H5Kb 4FR2lymYYWP8MtKyF4L/hlHZFCJWo2LA1LKYiiNs9bYlv5BxqKjGbhK5wCxqa/OZtU7m YTq+nOfk07P6Lop1mKbjHed+H0ovuJYlCSvDVnv8n5W3ClIXRlf5KNsMBt28JS6vp7vS kJhg== X-Forwarded-Encrypted: i=1; AJvYcCUvotTEuu4skANw1njQ97Zg7RqGekbCK8t5/MUwYMzr8UwtEb60FWvLUAkkQbiAtRUonX5UxCkt5HS0ig8=@vger.kernel.org X-Gm-Message-State: AOJu0Yy6C/W6nc/n1lFqYAauhV+VhCm5waqQaRCDZm3jymYIWsZogHWu WPMGtVDZYie92HWUh+vq6ycSrGAGSDADO8E8/Y0YJ2rxhIX39qLkJxcq X-Gm-Gg: AZuq6aKLTjWHAvtgdL/tYjNyym9du22yJmnkWYmAbmRrDIajED1cxPzvH3ihtYg6f7u 93b/frudCq3mkkuI/D2nFmNdvrOclWFd1EuE7U4i3A0P+u2tTnpuWHrifZJSRGEbdLt+5vaOpl3 ZbiJCVRRy+uOpkfQTld2s8qt85cKPYfgcA6KdnKR/TNiIpuCUIUtdfgTWwoSVTcp6Dm8Afw2ADe 0f11jBUxxrNwVGYj//BmF/gS0GJYICQPp0LNxxBLCPtuqqY3OjLcXjvFDhVHqdfhGeUONRmHoLC 3hSLuf6WuMf089T4til8GTYabu99so56tB5uaM+PHprgm1hJRBfbnd2lQpf7Fh9HkjyBWINdPB2 R0IXsQijMTMuN7BhiMG4pKsNSq7XtzamVA/7IYHGddKIO977LaJ9PT7YdXnyt2pSKsinUQeD3f/ +ZKBo= X-Received: by 2002:a05:693c:61d2:b0:2a4:3593:cca7 with SMTP id 5a478bee46e88-2b78e6beedbmr2168496eec.4.1769580388693; Tue, 27 Jan 2026 22:06:28 -0800 (PST) Received: from debian ([74.48.213.230]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b7a17083dasm1548275eec.14.2026.01.27.22.06.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Jan 2026 22:06:28 -0800 (PST) From: Qiliang Yuan To: Li Huafei , Andrew Morton , Ingo Molnar , Jinchao Wang , Yicong Yang , Qiliang Yuan , Thorsten Blum Cc: linux-watchdog@vger.kernel.org, mm-commits@vger.kernel.org, Shouxin Sun , Junnan Zhang , Song Liu , linux-kernel@vger.kernel.org Subject: [PATCH v7] watchdog/hardlockup: simplify perf event probe and remove per-cpu dependency Date: Wed, 28 Jan 2026 01:05:29 -0500 Message-ID: <20260128060544.1714875-1-realwujing@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Simplify the hardlockup detector's probe path and remove its implicit dependency on pinned per-cpu execution. Refactor hardlockup_detector_event_create() to be stateless. Return the created perf_event pointer to the caller instead of directly modifying the per-cpu 'watchdog_ev' variable. This allows the probe path to safely manage a temporary event without the risk of leaving stale pointers should task migration occur. Signed-off-by: Shouxin Sun Signed-off-by: Junnan Zhang Signed-off-by: Qiliang Yuan Cc: Song Liu Cc: Jinchao Wang --- v7: - Update Signed-off-by to match author email. - Remove redundant cpu_hotplug_disable() in probe path. - v6 link: https://lore.kernel.org/all/20260128023136.1691973-1-realwujing@= gmail.com/ v6: - Change title to "simplify/cleanup" and remove "Fixes" tag since the issue is not reproducible on mainline. - Rewrite commit message in imperative mood. - Clarify that mainline is safe while this improves robustness. - v5 link: https://lore.kernel.org/all/20260127022238.1182079-1-realwujing@= gmail.com/ v5: - Refine description: clarify that the retry path uses worker threads without PF_PERCPU_THREAD (though mainline is safe due to system_percpu_wq= ). - v4 link: https://lore.kernel.org/all/20260124070814.806828-1-realwujing@g= mail.com/ v4: - Add cpu_hotplug_disable() in watchdog_hardlockup_probe() to stabilize the probe CPU. - Update description to explain the relevance of 4.19 logs. v3: - Refactor hardlockup_detector_event_create() to be stateless by returning the event pointer instead of directly assigning to per-cpu variables. - Restore PMU cycle fallback and unify the enable/probe paths. v2: - Add Cc: stable@vger.kernel.org. v1: - Avoid 'watchdog_ev' in probe path by manually creating and releasing a local perf event. kernel/watchdog_perf.c | 51 ++++++++++++++++++++++++------------------ 1 file changed, 29 insertions(+), 22 deletions(-) diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c index d3ca70e3c256..4a798443033b 100644 --- a/kernel/watchdog_perf.c +++ b/kernel/watchdog_perf.c @@ -17,6 +17,7 @@ #include #include #include +#include =20 #include #include @@ -118,18 +119,11 @@ static void watchdog_overflow_callback(struct perf_ev= ent *event, watchdog_hardlockup_check(smp_processor_id(), regs); } =20 -static int hardlockup_detector_event_create(void) +static struct perf_event *hardlockup_detector_event_create(unsigned int cp= u) { - unsigned int cpu; struct perf_event_attr *wd_attr; struct perf_event *evt; =20 - /* - * Preemption is not disabled because memory will be allocated. - * Ensure CPU-locality by calling this in per-CPU kthread. - */ - WARN_ON(!is_percpu_thread()); - cpu =3D raw_smp_processor_id(); wd_attr =3D &wd_hw_attr; wd_attr->sample_period =3D hw_nmi_get_sample_period(watchdog_thresh); =20 @@ -143,14 +137,7 @@ static int hardlockup_detector_event_create(void) watchdog_overflow_callback, NULL); } =20 - if (IS_ERR(evt)) { - pr_debug("Perf event create on CPU %d failed with %ld\n", cpu, - PTR_ERR(evt)); - return PTR_ERR(evt); - } - WARN_ONCE(this_cpu_read(watchdog_ev), "unexpected watchdog_ev leak"); - this_cpu_write(watchdog_ev, evt); - return 0; + return evt; } =20 /** @@ -159,17 +146,26 @@ static int hardlockup_detector_event_create(void) */ void watchdog_hardlockup_enable(unsigned int cpu) { + struct perf_event *evt; + WARN_ON_ONCE(cpu !=3D smp_processor_id()); =20 - if (hardlockup_detector_event_create()) + evt =3D hardlockup_detector_event_create(cpu); + if (IS_ERR(evt)) { + pr_debug("Perf event create on CPU %d failed with %ld\n", cpu, + PTR_ERR(evt)); return; + } =20 /* use original value for check */ if (!atomic_fetch_inc(&watchdog_cpus)) pr_info("Enabled. Permanently consumes one hw-PMU counter.\n"); =20 + WARN_ONCE(this_cpu_read(watchdog_ev), "unexpected watchdog_ev leak"); + this_cpu_write(watchdog_ev, evt); + watchdog_init_timestamp(); - perf_event_enable(this_cpu_read(watchdog_ev)); + perf_event_enable(evt); } =20 /** @@ -263,19 +259,30 @@ bool __weak __init arch_perf_nmi_is_available(void) */ int __init watchdog_hardlockup_probe(void) { + struct perf_event *evt; + unsigned int cpu; int ret; =20 if (!arch_perf_nmi_is_available()) return -ENODEV; =20 - ret =3D hardlockup_detector_event_create(); + if (!hw_nmi_get_sample_period(watchdog_thresh)) + return -EINVAL; =20 - if (ret) { + /* + * Test hardware PMU availability by creating a temporary perf event. + * The event is released immediately. + */ + cpu =3D raw_smp_processor_id(); + evt =3D hardlockup_detector_event_create(cpu); + if (IS_ERR(evt)) { pr_info("Perf NMI watchdog permanently disabled\n"); + ret =3D PTR_ERR(evt); } else { - perf_event_release_kernel(this_cpu_read(watchdog_ev)); - this_cpu_write(watchdog_ev, NULL); + perf_event_release_kernel(evt); + ret =3D 0; } + return ret; } =20 --=20 2.51.0