From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Sebastian Siewior <bigeasy@linutronix.de>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
"David S. Miller" <davem@davemloft.net>,
Fenghua Yu <fenghua.yu@intel.com>,
Herbert Xu <herbert@gondor.apana.org.au>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Len Brown <lenb@kernel.org>,
Michael Ellerman <mpe@ellerman.id.au>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Tejun Heo <tj@kernel.org>, Tony Luck <tony.luck@intel.com>,
Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [patch 00/13] sched/treewide: Clean up various racy task affinity issues
Date: Thu, 13 Apr 2017 11:02:11 +0200 [thread overview]
Message-ID: <20170413090211.6h5cx2q3odmz5wcj@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20170412200726.941336635@linutronix.de>
On Wed, Apr 12, 2017 at 10:07:26PM +0200, Thomas Gleixner wrote:
> While dealing with the fallout of the scheduler cleanups on RT, we found
> several racy usage sites of the following scheme:
>
> cpumask_copy(&save_cpus_allowed, ¤t->cpus_allowed);
> set_cpus_allowed_ptr(current, cpumask_of(cpu));
> do_stuff();
> set_cpus_allowed_ptr(current, &save_cpus_allowed);
>
> That's racy in two aspects:
>
> 1) Nothing prevents the CPU from being unplugged after the temporary
> affinity setting is in place. This results on code being executed on the
> wrong CPU(s).
>
> 2) Nothing prevents a concurrent affinity setting from user space. That
> also results in code being executed on the wrong CPU(s) and the restore
> of the previous affinity setting overwrites the new one.
>
> Various variants of cleanups:
>
> - Removal, because the calling thread is already guaranteed to run on the
> correct CPU.
>
> - Conversion to smp function calls (simple register read/write)
>
> - Conversion to work_on_cpu(). There were even files containing comments
> to that effect.
>
> - The rest needs seperate hotplug protection for work_on_cpu(). To avoid open
> coding the
>
> get_online_cpus();
> if (cpu_online(cpu))
> ret = do_stuff();
> else
> ret = -ENODEV;
> put_online_cpus();
>
> scheme this series provides a new helper function work_on_cpu_safe()
> which implements the above.
>
> Aside of fixing these races this allows to restrict the access to
> current->cpus_allowed with a follow up series.
Looks good, thanks for tackling these!
prev parent reply other threads:[~2017-04-13 9:02 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-12 20:07 [patch 00/13] sched/treewide: Clean up various racy task affinity issues Thomas Gleixner
2017-04-12 20:07 ` [patch 01/13] ia64/topology: Remove cpus_allowed manipulation Thomas Gleixner
2017-04-15 14:15 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 02/13] workqueue: Provide work_on_cpu_safe() Thomas Gleixner
2017-04-13 11:11 ` Dou Liyang
2017-04-13 21:28 ` Thomas Gleixner
2017-04-14 4:18 ` Tejun Heo
2017-04-14 8:54 ` Peter Zijlstra
2017-04-14 9:51 ` Thomas Gleixner
2017-04-14 9:56 ` Peter Zijlstra
2017-04-15 14:16 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 03/13] ia64/salinfo: Replace racy task affinity logic Thomas Gleixner
2017-04-15 14:17 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 04/13] ia64/sn/hwperf: " Thomas Gleixner
2017-04-12 20:53 ` [patch V 2 " Thomas Gleixner
2017-04-15 14:17 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 05/13] powerpc/smp: Replace open coded " Thomas Gleixner
2017-04-13 5:47 ` Michael Ellerman
2017-04-15 14:18 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 06/13] sparc/sysfs: Replace racy " Thomas Gleixner
2017-04-13 1:52 ` David Miller
2017-04-13 8:17 ` [patch V2 " Thomas Gleixner
2017-04-15 14:18 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 07/13] ACPI/processor: Fix error handling in __acpi_processor_start() Thomas Gleixner
2017-04-15 14:19 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 08/13] ACPI/processor: Replace racy task affinity logic Thomas Gleixner
2017-04-13 11:39 ` Peter Zijlstra
2017-04-13 12:01 ` Thomas Gleixner
2017-04-13 12:52 ` Peter Zijlstra
2017-04-15 14:19 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 09/13] cpufreq/ia64: " Thomas Gleixner
2017-04-12 20:55 ` [patch V2 " Thomas Gleixner
2017-04-15 14:20 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-13 2:42 ` [patch 09/13] " Viresh Kumar
2017-04-12 20:07 ` [patch 10/13] cpufreq/sh: " Thomas Gleixner
2017-04-13 2:46 ` Viresh Kumar
2017-04-15 14:20 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 11/13] cpufreq/sparc-us3: " Thomas Gleixner
2017-04-13 2:48 ` Viresh Kumar
2017-04-15 14:21 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-12 20:07 ` [patch 12/13] cpufreq/sparc-us2e: " Thomas Gleixner
2017-04-13 2:50 ` Viresh Kumar
2017-04-13 8:19 ` [patch V2 " Thomas Gleixner
2017-04-13 8:22 ` [patch V3 " Thomas Gleixner
2017-04-15 14:21 ` [tip:sched/core] " tip-bot for Thomas Gleixner
2017-04-13 14:50 ` [patch V2 12/13] " David Miller
2017-04-12 20:07 ` [patch 13/13] crypto: n2 - " Thomas Gleixner
2017-04-13 4:56 ` Herbert Xu
2017-04-13 8:20 ` [patch V2 " Thomas Gleixner
2017-04-13 14:51 ` David Miller
2017-04-15 14:22 ` [tip:sched/core] crypto: N2 " tip-bot for Thomas Gleixner
2017-04-13 9:02 ` Peter Zijlstra [this message]
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