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[2a02:3100:ad43:d501:2c28:bb72:120d:420e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a203b4f9d9sm43385995e9.11.2026.10.21.22.43.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2026 22:43:13 -0700 (PDT) Date: Thu, 22 Oct 2026 07:43:11 +0200 From: Karl Mehltretter To: Thomas Gleixner Cc: John Stultz , Stephen Boyd , Miroslav Lichvar , Jiri Wiesner , Daniel J Blueman , regressions@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [REGRESSION] clocksource: delayed watchdog can mark TSC unstable Message-ID: References: <20261010065509.72916-1-kmehltretter@gmail.com> <87a4oeerwm.ffs@fw13> X-Mailing-List: regressions@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a4oeerwm.ffs@fw13> On Thu, Oct 15, 2026 at 08:32:25PM +0100, Thomas Gleixner wrote: > > busybox-79 [000] ..s1. 15.168486: clocksource_watchdog <-call_timer_fn > > busybox-79 [000] .Ns.. 16.269726: clocksource_watchdog <-call_timer_fn > > busybox-79 [000] .Ns.. 16.269820: clocksource_watchdog <-call_timer_fn > > I did not think about that scenario obvioulsy. The code is resilient > against long intervals between two measurements, so the easy and > straight forward fix is indeed what you (or the LLM) suggested. > > Thanks, > > tglx > --- > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -673,7 +673,7 @@ static void clocksource_watchdog(struct > > /* Could have been rearmed by a stop/start cycle */ > if (!timer_pending(&watchdog_timer)) { > - watchdog_timer.expires += WATCHDOG_INTERVAL; > + watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; > add_timer_local(&watchdog_timer); > } > } Yes, I tested this change on v7.3-rc5 (72d3fcf802c4) baseline patched TSC marked unstable 2/3 boots 0/3 boots watchdog gaps below 250 ms 3/3 boots 0/3 boots minimum traced gap 0.231 ms 505.484 ms Each boot had four QEMU TCG vCPUs. I used PTRACE_ATTACH to stop only the vCPU 0 TCG thread for 800 ms. Thanks, Karl