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Fri, 06 Nov 2026 02:26:40 -0800 (PST) Received: from [192.168.1.107] ([203.221.253.165]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36fa651e6b1sm11482680eec.3.2026.11.06.02.26.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Nov 2026 02:26:39 -0800 (PST) From: Michael Ellerman X-Google-Original-From: Michael Ellerman Message-ID: <9fada7bf-11b5-45b6-858d-4c6b79d6a507@kernel.org> Date: Fri, 6 Nov 2026 21:26:34 +1100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] powerpc/watchdog: disable watchdog when watchdog_thresh=0 To: "Luiz Capitulino (Red Hat)" , maddy@linux.ibm.com, npiggin@gmail.com, linuxppc-dev@lists.ozlabs.org Cc: chleroy@kernel.org, ritesh.list@gmail.com, sshegde@linux.ibm.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org References: <20261104034018.2676750-1-luiz.capitulino@linux.dev> Content-Language: en-US In-Reply-To: <20261104034018.2676750-1-luiz.capitulino@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/11/26 2:40 pm, Luiz Capitulino (Red Hat) wrote: > On powerpc, trying to disable the hardlockup detector with: > > # echo 0 > /proc/sys/kernel/watchdog_thresh > > causes an immediate and endless hardlockup detection, eventually leading > to an unusable system (splat example below). ... > This condition is already checked in __lockup_detector_reconfigure() for > the soft lockup detector and the arch-independent hardlockup detector, > what's missing is powerpc performing the same check in start_watchdog(). Arguably setting watchdog_thresh to 0 should mean watchdog_enabled becomes false. Then there wouldn't need to be extra checks for thresh == 0 anywhere. But if the existing code already checks for thresh == 0 then this is fine. > Fixes: 2104180a5369 ("powerpc/64s: implement arch-specific hardlockup watchdog") > Cc: stable@vger.kernel.org > Signed-off-by: Luiz Capitulino (Red Hat) > --- > Notes: > - This issue was not discovered by AI. We have a new test-case in our CI that > sets watchdog_thresh=0, when running on powerpc we get the described issue > - This issue was initially reproduced on Power10, but I developed the fix > on Power9 (which is what I have access now) > > arch/powerpc/kernel/watchdog.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c > index 582ee3fd71c1..44f178e07531 100644 > --- a/arch/powerpc/kernel/watchdog.c > +++ b/arch/powerpc/kernel/watchdog.c > @@ -487,6 +487,9 @@ static void start_watchdog(void *arg) > if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED)) > return; > > + if (!watchdog_thresh) > + return; > + > if (!cpumask_test_cpu(cpu, &watchdog_cpumask)) > return; Fix looks good to me. Reviewed-by: Michael Ellerman cheers