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Message-ID: <20240618150417.kuoft7jqqg6pcjrf@airbuntu>
Date: Tue, 18 Jun 2024 16:04:17 +0100
From: Qais Yousef <qyousef@...alina.io>
To: John Stultz <jstultz@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Frederic Weisbecker <frederic@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
Joel Fernandes <joel@...lfernandes.org>, kernel-team@...roid.com
Subject: Re: [PATCH] RFC: sched: Rework task_sched_runtime to avoid calling
update_rq_clock
On 06/17/24 21:45, John Stultz wrote:
> On Mon, Jun 17, 2024 at 5:42 PM John Stultz <jstultz@...gle.com> wrote:
> >
> > Also, separately, while I didn't see this earlier testing on physical
> > devices, when running virtualized, I can pretty easily trip over the
> > following:
> >
> > [ 65.207340] watchdog: BUG: soft lockup - CPU#0 stuck for 26s!
> > [kworker/0:3:374]
> > [ 65.211107] irq event stamp: 118664
> > [ 65.212786] hardirqs last enabled at (118663):
> > [<ffffffff97a00e46>] asm_sysvec_apic_timer_interrupt+0x16/0x20
> > [ 65.218440] hardirqs last disabled at (118664):
> > [<ffffffff977fdeca>] sysvec_apic_timer_interrupt+0xa/0xc0
> > [ 65.223074] softirqs last enabled at (118546):
> > [<ffffffff9676db78>] __irq_exit_rcu+0x88/0xe0
> > [ 65.227118] softirqs last disabled at (118541):
> > [<ffffffff9676db78>] __irq_exit_rcu+0x88/0xe0
> > [ 65.231137] CPU: 0 PID: 374 Comm: kworker/0:3 Not tainted
> > 6.10.0-rc4-dirty #4393
> > [ 65.234625] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> > BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> > [ 65.239089] Workqueue: events psi_avgs_work
> > [ 65.241122] RIP: 0010:collect_percpu_times+0xff/0x310
> ...
> > [ 65.288730] Call Trace:
> > [ 65.289958] <IRQ>
> > [ 65.290965] ? watchdog_timer_fn+0x275/0x310
> > [ 65.293185] ? __pfx_watchdog_timer_fn+0x10/0x10
> > [ 65.295379] ? __hrtimer_run_queues+0x190/0x3b0
> > [ 65.297795] ? hrtimer_interrupt+0xf9/0x230
> > [ 65.299782] ? __sysvec_apic_timer_interrupt+0x82/0x210
> > [ 65.302243] ? sysvec_apic_timer_interrupt+0x98/0xc0
> > [ 65.304590] </IRQ>
> > [ 65.305658] <TASK>
> > [ 65.306708] ? asm_sysvec_apic_timer_interrupt+0x16/0x20
> > [ 65.309206] ? psi_avgs_work+0x3c/0xb0
> > [ 65.311001] ? collect_percpu_times+0xff/0x310
> > [ 65.313153] psi_avgs_work+0x3c/0xb0
> > [ 65.314864] process_one_work+0x1fe/0x700
> > [ 65.316782] ? lock_is_held_type+0xcd/0x120
> > [ 65.318782] worker_thread+0x1c7/0x3b0
> > [ 65.320571] ? __pfx_worker_thread+0x10/0x10
> > [ 65.322626] kthread+0xe0/0x110
> > [ 65.324103] ? __pfx_kthread+0x10/0x10
> > [ 65.325853] ret_from_fork+0x28/0x40
> > [ 65.327512] ? __pfx_kthread+0x10/0x10
> > [ 65.329255] ret_from_fork_asm+0x1a/0x30
> > [ 65.331073] </TASK>
> > [ 65.332119] Kernel panic - not syncing: softlockup: hung tasks
>
> As I've been digging on this some more, I'm still a bit baffled. The
> kworker seems to get stuck once the irq lands and we don't seem to go
> back to the workqueue work that was in progress. That cpu ends up not
> doing anything but occasionally handling ticks until we crash from the
> softlockup watchdog.
>
> Interestingly, if I move the psi_account_irqtime() call to be under
> the rq_lock in sched_tick(), as I suggested earlier, I have yet to
> reproduce the problem.
> But I'm still trying to piece together exactly why.
A bit of a guess, but should irq_time_read() be done with interrupts disabled?
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