linux-kernel - Re: [PATCH] clocksource: Skip watchdog check for large watchdog intervals

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Message-ID: <20240110183618.GG3303@incl>
Date: Wed, 10 Jan 2024 19:36:18 +0100
From: Jiri Wiesner <jwiesner@...e.de>
To: linux-kernel@...r.kernel.org
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com, Feng Tang <feng.tang@...el.com>,
	John Stultz <jstultz@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] clocksource: Skip watchdog check for large watchdog
 intervals

On Mon, Jan 08, 2024 at 09:44:31PM +0800, kernel test robot wrote:
> commit: ceacf0b27b5d9cdc574f8d0a0bcb11d3272e7b9f ("[PATCH] clocksource: Skip watchdog check for large watchdog intervals")
> url: https://github.com/intel-lab-lkp/linux/commits/Jiri-Wiesner/clocksource-Skip-watchdog-check-for-large-watchdog-intervals/20240103-192257
> base: https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git da65f29dada7f7cbbf0d6375b88a0316f5f7d6f5
> patch link: https://lore.kernel.org/all/20240103112113.GA6108@incl/
> patch subject: [PATCH] clocksource: Skip watchdog check for large watchdog intervals
> 
> [   54.778895][   T41] ------------[ cut here ]------------
> [ 54.781279][ T41] WARNING: CPU: 0 PID: 41 at kernel/time/clocksource-wdtest.c:162 wdtest_func (kernel/time/clocksource-wdtest.c:162 (discriminator 1)) 
> [   54.785405][   T41] Modules linked in:
> [   54.787152][   T41] CPU: 0 PID: 41 Comm: wdtest Tainted: G                 N 6.7.0-rc2-00014-gceacf0b27b5d #1 30e4ebd22e7da702dfdab1313ae74e5a246df970
> [   54.791633][   T41] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [ 54.795124][ T41] EIP: wdtest_func (kernel/time/clocksource-wdtest.c:162 (discriminator 1)) 

The code:
        pr_info("--- Watchdog clock-value-fuzz error injection, expect clock skew and per-CPU mismatches.\n");
        WRITE_ONCE(wdtest_ktime_read_fuzz, true);
        schedule_timeout_uninterruptible(2 * HZ);
        WARN_ON_ONCE(!(clocksource_wdtest_ktime.flags & CLOCK_SOURCE_UNSTABLE));

The warning is the consequence of the watchdog not running on i386 builds of the kernel. The watchdog does not run because the "interval > WATCHDOG_INTR_MAX_NS" check is always true on account of the WATCHDOG_INTR_MAX_NS constant evaluating to a negative number on account of integer overflow.

> [   54.801794][   T41] EAX: c4a1fe8c EBX: 00000004 ECX: 00000000 EDX: 00000000
> [   54.803569][   T41] ESI: c4a1ff2e EDI: 00000000 EBP: c74aff70 ESP: c74aff60
> [   54.805314][   T41] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010246
> [   54.807278][   T41] CR0: 80050033 CR2: ffda9000 CR3: 05979000 CR4: 000406d0
> [   54.808856][   T41] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> [   54.810216][   T41] DR6: fffe0ff0 DR7: 00000400
> [   54.811218][   T41] Call Trace:

-- 
Jiri Wiesner
SUSE Labs