From: Thomas Gleixner <tglx@linutronix.de>
To: paulmck@kernel.org
Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org,
sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com,
maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org,
ak@linux.intel.com
Subject: Re: [PATCH v7 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable
Date: Mon, 12 Apr 2021 15:08:16 +0200 [thread overview]
Message-ID: <87k0p71whr.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210412042157.GA1889369@paulmck-ThinkPad-P17-Gen-1>
On Sun, Apr 11 2021 at 21:21, Paul E. McKenney wrote:
> On Sun, Apr 11, 2021 at 09:46:12AM -0700, Paul E. McKenney wrote:
>> So I need to is inline clocksource_verify_percpu_wq()
>> into clocksource_verify_percpu() and then move the call to
>> clocksource_verify_percpu() to __clocksource_watchdog_kthread(), right
>> before the existing call to list_del_init(). Will do!
>
> Except that this triggers the WARN_ON_ONCE() in smp_call_function_single()
> due to interrupts being disabled across that list_del_init().
>
> Possibilities include:
>
> 1. Figure out why interrupts must be disabled only sometimes while
> holding watchdog_lock, in the hope that they need not be across
> the entire critical section for __clocksource_watchdog_kthread().
> As in:
>
> local_irq_restore(flags);
> clocksource_verify_percpu(cs);
> local_irq_save(flags);
>
> Trying this first with lockdep enabled. Might be spectacular.
Yes, it's a possible deadlock against the watchdog timer firing ...
The reason for irqsave is again historical AFAICT and nobody bothered to
clean it up. spin_lock_bh() should be sufficient to serialize against
the watchdog timer, though I haven't looked at all possible scenarios.
> 2. Invoke clocksource_verify_percpu() from its original
> location in clocksource_watchdog(), just before the call to
> __clocksource_unstable(). This relies on the fact that
> clocksource_watchdog() acquires watchdog_lock without
> disabling interrupts.
That should be fine, but this might cause the softirq to 'run' for a
very long time which is not pretty either.
Aside of that, do we really need to check _all_ online CPUs? What you
are trying to figure out is whether the wreckage is CPU local or global,
right?
Wouldn't a shirt-sleeve approach of just querying _one_ CPU be good
enough? Either the other CPU has the same wreckage, then it's global or
it hasn't which points to a per CPU local issue.
Sure it does not catch the case where a subset (>1) of all CPUs is
affected, but I'm not seing how that really buys us anything.
Thanks,
tglx
next prev parent reply other threads:[~2021-04-12 13:08 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 0:40 [PATCH RFC clocksource] Do not mark clocks unstable due to delays Paul E. McKenney
2021-01-06 0:41 ` [PATCH RFC clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog paulmck
2021-01-06 0:41 ` [PATCH RFC clocksource 2/5] clocksource: Retry clock read if long delays detected paulmck
2021-01-06 16:28 ` Rik van Riel
2021-01-06 19:53 ` Paul E. McKenney
2021-01-06 20:59 ` Rik van Riel
2021-01-06 0:41 ` [PATCH RFC clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-01-06 0:41 ` [PATCH RFC clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-01-06 0:41 ` [PATCH RFC clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking paulmck
2021-01-12 0:42 ` [PATCH v2 clocksource] Do not mark clocks unstable due to delays Paul E. McKenney
2021-01-12 0:45 ` [PATCH v2 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog paulmck
2021-01-12 0:45 ` [PATCH v2 clocksource 2/5] clocksource: Retry clock read if long delays detected paulmck
2021-01-12 0:45 ` [PATCH v2 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-01-12 0:45 ` [PATCH v2 clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-01-12 0:45 ` [PATCH v2 clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking paulmck
2021-02-02 17:04 ` [PATCH v3 clocksource] Do not mark clocks unstable due to delays Paul E. McKenney
2021-02-02 17:06 ` [PATCH clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog paulmck
2021-02-02 17:06 ` [PATCH clocksource 2/5] clocksource: Retry clock read if long delays detected paulmck
2021-02-02 17:06 ` [PATCH clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-02-02 17:06 ` [PATCH clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-02-02 19:51 ` Randy Dunlap
2021-02-03 0:50 ` Paul E. McKenney
2021-02-03 1:31 ` Randy Dunlap
2021-02-03 1:40 ` Paul E. McKenney
2021-02-02 17:06 ` [PATCH clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking paulmck
2021-02-17 21:28 ` [PATCH v3 clocksource] Do not mark clocks unstable due to delays Paul E. McKenney
2021-02-17 21:29 ` [PATCH clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog paulmck
2021-02-17 21:29 ` [PATCH clocksource 2/5] clocksource: Retry clock read if long delays detected paulmck
2021-02-17 21:29 ` [PATCH clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-02-17 21:29 ` [PATCH clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-02-17 21:29 ` [PATCH clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking paulmck
2021-03-04 0:49 ` [PATCH v5 clocksource] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-03-04 0:53 ` [PATCH kernel/time 1/5] clocksource: Provide module parameters to inject delays in watchdog paulmck
2021-03-04 0:53 ` [PATCH kernel/time 2/5] clocksource: Retry clock read if long delays detected paulmck
2021-03-04 0:53 ` [PATCH kernel/time 3/5] clocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-03-04 0:53 ` [PATCH kernel/time 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-03-04 0:53 ` [PATCH kernel/time 5/5] clocksource: Do pairwise clock-desynchronization checking paulmck
2021-04-02 20:29 ` [PATCH v5 clocksource] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-04-02 20:31 ` [PATCH v6 clocksource] Do not mark clocks unstable dueclocksource: Provide module parameters to inject delays in watchdog paulmck
2021-04-02 22:22 ` Thomas Gleixner
2021-04-02 22:37 ` Paul E. McKenney
2021-04-02 22:48 ` [PATCH v7 clocksource] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-04-02 22:49 ` [PATCH v7 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog paulmck
2021-04-02 22:49 ` [PATCH v7 clocksource 2/5] clocksource: Retry clock read if long delays detected paulmck
2021-04-10 8:41 ` Thomas Gleixner
2021-04-10 23:50 ` Paul E. McKenney
2021-04-02 22:49 ` [PATCH v7 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-04-10 9:00 ` Thomas Gleixner
2021-04-11 0:20 ` Paul E. McKenney
2021-04-11 10:33 ` Thomas Gleixner
2021-04-11 16:46 ` Paul E. McKenney
2021-04-12 4:21 ` Paul E. McKenney
2021-04-12 13:08 ` Thomas Gleixner [this message]
2021-04-12 18:20 ` Paul E. McKenney
2021-04-12 18:54 ` Thomas Gleixner
2021-04-12 19:57 ` Paul E. McKenney
2021-04-12 20:37 ` Thomas Gleixner
2021-04-12 23:18 ` Paul E. McKenney
2021-04-13 20:49 ` Thomas Gleixner
2021-04-14 4:48 ` Paul E. McKenney
2021-04-02 22:49 ` [PATCH v7 clocksource 4/5] clocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-04-02 22:49 ` [PATCH v7 clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking paulmck
2021-04-10 9:04 ` Thomas Gleixner
2021-04-11 0:21 ` Paul E. McKenney
2021-04-10 8:01 ` [PATCH v7 clocksource] Do not mark clocks unstable due to delays for v5.13 Thomas Gleixner
2021-04-10 23:26 ` Paul E. McKenney
2021-04-11 10:58 ` Thomas Gleixner
2021-04-11 16:50 ` Paul E. McKenney
2021-04-02 20:31 ` [PATCH v6 clocksource] Do not mark clocks unstable dueclocksource: Retry clock read if long delays detected paulmck
2021-04-02 20:31 ` [PATCH v6 clocksource] Do not mark clocks unstable dueclocksource: Check per-CPU clock synchronization when marked unstable paulmck
2021-04-02 20:31 ` [PATCH v6 clocksource] Do not mark clocks unstable dueclocksource: Provide a module parameter to fuzz per-CPU clock checking paulmck
2021-04-02 20:31 ` [PATCH v6 clocksource] Do not mark clocks unstable dueclocksource: Do pairwise clock-desynchronization checking paulmck
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