linux-kernel - Re: [PATCH] wq: handle VM suspension in stall detection

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Date:   Thu, 20 May 2021 12:59:07 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org,
        Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH] wq: handle VM suspension in stall detection

On Thu, May 20, 2021 at 07:14:22PM +0900, Sergey Senozhatsky wrote:
> If VCPU is suspended (VM suspend) in wq_watchdog_timer_fn() then
> once this VCPU resumes it will see the new jiffies value, while it
> may take a while before IRQ detects PVCLOCK_GUEST_STOPPED on this
> VCPU and updates all the watchdogs via pvclock_touch_watchdogs().
> There is a small chance of misreported WQ stalls in the meantime,
> because new jiffies is time_after() old 'ts + thresh'.
> 
> wq_watchdog_timer_fn()
> {
> 	for_each_pool(pool, pi) {
> 		if (time_after(jiffies, ts + thresh)) {
> 			pr_emerg("BUG: workqueue lockup - pool");
> 		}
> 	}
> }
> 
> Save jiffies at the beginning of this function and use that value
> for stall detection. If VM gets suspended then we continue using
> "old" jiffies value and old WQ touch timestamps. If IRQ at some
> point restarts the stall detection cycle (pvclock_touch_watchdogs())
> then old jiffies will always be before new 'ts + thresh'.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>

Applied to wq/for-5.13-fixes.

Thanks.

-- 
tejun