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From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@gentwo.org>,
	Sasha Levin <sasha.levin@oracle.com>,
	akpm@linux-foundation.org, Gilad Ben-Yossef <gilad@benyossef.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	John Stultz <johnstul@us.ibm.com>,
	Mike Frysinger <vapier@gentoo.org>,
	Minchan Kim <minchan.kim@gmail.com>,
	Hakan Akkan <hakanakkan@gmail.com>,
	Max Krasnyansky <maxk@qualcomm.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	hughd@google.com, viresh.kumar@linaro.org, hpa@zytor.com,
	mingo@kernel.org
Subject: Re: vmstat: On demand vmstat workers V8
Date: Tue, 29 Jul 2014 14:23:03 +0200	[thread overview]
Message-ID: <20140729122303.GA3935@laptop> (raw)
In-Reply-To: <20140729120525.GA28366@mtj.dyndns.org>

On Tue, Jul 29, 2014 at 08:05:25AM -0400, Tejun Heo wrote:
> On Tue, Jul 29, 2014 at 09:56:37AM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 28, 2014 at 01:55:17PM -0500, Christoph Lameter wrote:
> > > On Fri, 25 Jul 2014, Sasha Levin wrote:
> > > 
> > > > This patch doesn't interact well with my fuzzing setup. I'm seeing
> > > > the following:
> > > >
> > > > [  490.446927] BUG: using __this_cpu_read() in preemptible [00000000] code: kworker/16:1/7368
> > > > [  490.447909] caller is __this_cpu_preempt_check+0x13/0x20
> > > 
> > > __this_cpu_read() from vmstat_update is only called from a kworker that
> > > is bound to a single cpu. A false positive?
> > 
> > kworkers are never guaranteed to be so, its a 'feature' :/
> 
> It's because we don't distinguish work items which are per-cpu for
> optimization and per-cpu for correctness and can't automatically flush
> / cancel / block per-cpu work items when a cpu goes down.  I like the
> idea of distingushing them but it's gonna take a lot of auditing.

Just force flush on unplug and fix those that complain. No auditing
needed for that.

> Any work item usage which requires per-cpu for correctness should
> implement cpu down hook to flush in-flight work items and block
> further issuance.  This hasn't changed from the beginning and was
> necessary even before cmwq.

I think before cmwq we'd run into the broken affinity warning in the
scheduler.

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@gentwo.org>,
	Sasha Levin <sasha.levin@oracle.com>,
	akpm@linux-foundation.org, Gilad Ben-Yossef <gilad@benyossef.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	John Stultz <johnstul@us.ibm.com>,
	Mike Frysinger <vapier@gentoo.org>,
	Minchan Kim <minchan.kim@gmail.com>,
	Hakan Akkan <hakanakkan@gmail.com>,
	Max Krasnyansky <maxk@qualcomm.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	hughd@google.com, viresh.kumar@linaro.org, hpa@zytor.com,
	mingo@kernel.org
Subject: Re: vmstat: On demand vmstat workers V8
Date: Tue, 29 Jul 2014 14:23:03 +0200	[thread overview]
Message-ID: <20140729122303.GA3935@laptop> (raw)
In-Reply-To: <20140729120525.GA28366@mtj.dyndns.org>

On Tue, Jul 29, 2014 at 08:05:25AM -0400, Tejun Heo wrote:
> On Tue, Jul 29, 2014 at 09:56:37AM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 28, 2014 at 01:55:17PM -0500, Christoph Lameter wrote:
> > > On Fri, 25 Jul 2014, Sasha Levin wrote:
> > > 
> > > > This patch doesn't interact well with my fuzzing setup. I'm seeing
> > > > the following:
> > > >
> > > > [  490.446927] BUG: using __this_cpu_read() in preemptible [00000000] code: kworker/16:1/7368
> > > > [  490.447909] caller is __this_cpu_preempt_check+0x13/0x20
> > > 
> > > __this_cpu_read() from vmstat_update is only called from a kworker that
> > > is bound to a single cpu. A false positive?
> > 
> > kworkers are never guaranteed to be so, its a 'feature' :/
> 
> It's because we don't distinguish work items which are per-cpu for
> optimization and per-cpu for correctness and can't automatically flush
> / cancel / block per-cpu work items when a cpu goes down.  I like the
> idea of distingushing them but it's gonna take a lot of auditing.

Just force flush on unplug and fix those that complain. No auditing
needed for that.

> Any work item usage which requires per-cpu for correctness should
> implement cpu down hook to flush in-flight work items and block
> further issuance.  This hasn't changed from the beginning and was
> necessary even before cmwq.

I think before cmwq we'd run into the broken affinity warning in the
scheduler.

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  reply	other threads:[~2014-07-29 12:23 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-10 14:04 vmstat: On demand vmstat workers V8 Christoph Lameter
2014-07-10 14:04 ` Christoph Lameter
2014-07-11 13:20 ` Frederic Weisbecker
2014-07-11 13:20   ` Frederic Weisbecker
2014-07-11 13:56   ` Christoph Lameter
2014-07-11 13:56     ` Christoph Lameter
2014-07-11 13:58     ` Frederic Weisbecker
2014-07-11 13:58       ` Frederic Weisbecker
2014-07-11 15:17       ` Christoph Lameter
2014-07-11 15:17         ` Christoph Lameter
2014-07-11 15:19         ` Frederic Weisbecker
2014-07-11 15:19           ` Frederic Weisbecker
2014-07-11 15:22           ` Christoph Lameter
2014-07-11 15:22             ` Christoph Lameter
2014-07-14 20:10             ` Hugh Dickins
2014-07-14 20:10               ` Hugh Dickins
2014-07-14 20:51               ` Christoph Lameter
2014-07-14 20:51                 ` Christoph Lameter
2014-07-30  3:04         ` Lai Jiangshan
2014-07-30  3:04           ` Lai Jiangshan
2014-07-26  2:22 ` Sasha Levin
2014-07-26  2:22   ` Sasha Levin
2014-07-28 18:55   ` Christoph Lameter
2014-07-28 18:55     ` Christoph Lameter
2014-07-28 21:54     ` Andrew Morton
2014-07-28 21:54       ` Andrew Morton
2014-07-28 22:00       ` Sasha Levin
2014-07-28 22:00         ` Sasha Levin
2014-07-29 15:17       ` Christoph Lameter
2014-07-29 15:17         ` Christoph Lameter
2014-07-29  7:56     ` Peter Zijlstra
2014-07-29 12:05       ` Tejun Heo
2014-07-29 12:05         ` Tejun Heo
2014-07-29 12:23         ` Peter Zijlstra [this message]
2014-07-29 12:23           ` Peter Zijlstra
2014-07-29 13:12           ` Tejun Heo
2014-07-29 13:12             ` Tejun Heo
2014-07-29 15:10             ` Christoph Lameter
2014-07-29 15:10               ` Christoph Lameter
2014-07-29 15:14               ` Tejun Heo
2014-07-29 15:14                 ` Tejun Heo
2014-07-29 15:26                 ` Christoph Lameter
2014-07-29 15:26                   ` Christoph Lameter
2014-07-29 15:39                 ` Christoph Lameter
2014-07-29 15:39                   ` Christoph Lameter
2014-07-29 15:47                   ` Sasha Levin
2014-07-29 15:47                     ` Sasha Levin
2014-07-29 15:59                     ` Christoph Lameter
2014-07-29 15:59                       ` Christoph Lameter
2014-07-30  3:11                   ` Lai Jiangshan
2014-07-30  3:11                     ` Lai Jiangshan
2014-07-30 14:34                     ` Christoph Lameter
2014-07-30 14:34                       ` Christoph Lameter
2014-07-29 15:22             ` Christoph Lameter
2014-07-29 15:22               ` Christoph Lameter
2014-07-29 15:43               ` Sasha Levin
2014-07-29 15:43                 ` Sasha Levin
2014-08-04 21:37   ` Sasha Levin
2014-08-04 21:37     ` Sasha Levin
2014-08-05 14:51     ` Christoph Lameter
2014-08-05 14:51       ` Christoph Lameter
2014-08-05 22:25       ` Sasha Levin
2014-08-05 22:25         ` Sasha Levin
2014-08-06 14:12         ` Christoph Lameter
2014-08-06 14:12           ` Christoph Lameter
2014-08-07  1:50           ` Sasha Levin
2014-08-07  1:50             ` Sasha Levin
2014-07-30  2:57 ` Lai Jiangshan
2014-07-30  2:57   ` Lai Jiangshan
2014-07-30 14:45   ` Christoph Lameter
2014-07-30 14:45     ` Christoph Lameter
2014-07-31  0:52     ` Lai Jiangshan
2014-07-31  0:52       ` Lai Jiangshan

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