Re: [patch 00/13] sched/treewide: Clean up various racy task affinity issues

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [patch 00/13] sched/treewide: Clean up various racy task affinity issues
Date	2017-04-13 11:10 +0200
Message-ID	<tvIVk-M6-11@gated-at.bofh.it> (permalink)
References	<tvx3P-QV-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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, &current->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!

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[patch 00/13] sched/treewide: Clean up various racy task affinity  issues Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
  [patch 12/13] cpufreq/sparc-us2e: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 12/13] cpufreq/sparc-us2e: Replace racy task affinity  logic Viresh Kumar <viresh.kumar@linaro.org> - 2017-04-13 05:00 +0200
    [patch V2 12/13] cpufreq/sparc-us2e: Replace racy task affinity  logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-13 10:20 +0200
      [patch V3 12/13] cpufreq/sparc-us2e: Replace racy task affinity  logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-13 10:30 +0200
        [tip:sched/core] cpufreq/sparc-us2e: Replace racy task affinity  logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
      Re: [patch V2 12/13] cpufreq/sparc-us2e: Replace racy task  affinity logic David Miller <davem@davemloft.net> - 2017-04-13 17:00 +0200
  [patch 03/13] ia64/salinfo: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    [tip:sched/core] ia64/salinfo: Replace racy task affinity logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 04/13] ia64/sn/hwperf: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    [patch V 2 04/13] ia64/sn/hwperf: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 23:00 +0200
      [tip:sched/core] ia64/sn/hwperf: Replace racy task affinity logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 11/13] cpufreq/sparc-us3: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 11/13] cpufreq/sparc-us3: Replace racy task affinity logic Viresh Kumar <viresh.kumar@linaro.org> - 2017-04-13 04:50 +0200
    [tip:sched/core] cpufreq/sparc-us3: Replace racy task affinity  logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 01/13] ia64/topology: Remove cpus_allowed manipulation Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    [tip:sched/core] ia64/topology: Remove cpus_allowed manipulation tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 07/13] ACPI/processor: Fix error handling in  __acpi_processor_start() Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    [tip:sched/core] ACPI/processor: Fix error handling in  __acpi_processor_start() tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 08/13] ACPI/processor: Replace racy task affinity logic. Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 08/13] ACPI/processor: Replace racy task affinity logic. Peter Zijlstra <peterz@infradead.org> - 2017-04-13 13:50 +0200
      Re: [patch 08/13] ACPI/processor: Replace racy task affinity  logic. Thomas Gleixner <tglx@linutronix.de> - 2017-04-13 14:10 +0200
        Re: [patch 08/13] ACPI/processor: Replace racy task affinity logic. Peter Zijlstra <peterz@infradead.org> - 2017-04-13 15:00 +0200
    [tip:sched/core] ACPI/processor: Replace racy task affinity logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 13/13] crypto: n2 - Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 13/13] crypto: n2 - Replace racy task affinity logic Herbert Xu <herbert@gondor.apana.org.au> - 2017-04-13 07:40 +0200
    [patch V2 13/13] crypto: n2 - Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-13 10:30 +0200
      Re: [patch V2 13/13] crypto: n2 - Replace racy task affinity logic David Miller <davem@davemloft.net> - 2017-04-13 17:00 +0200
      [tip:sched/core] crypto: N2 - Replace racy task affinity logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:40 +0200
  [patch 05/13] powerpc/smp: Replace open coded task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 05/13] powerpc/smp: Replace open coded task affinity logic Michael Ellerman <mpe@ellerman.id.au> - 2017-04-13 07:50 +0200
    [tip:sched/core] powerpc/smp: Replace open coded task affinity  logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  [patch 06/13] sparc/sysfs: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 06/13] sparc/sysfs: Replace racy task affinity logic David Miller <davem@davemloft.net> - 2017-04-13 04:00 +0200
      [patch V2 06/13] sparc/sysfs: Replace racy task affinity logic Thomas Gleixner <tglx@linutronix.de> - 2017-04-13 10:20 +0200
        [tip:sched/core] sparc/sysfs: Replace racy task affinity logic tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:20 +0200
  [patch 02/13] workqueue: Provide work_on_cpu_safe() Thomas Gleixner <tglx@linutronix.de> - 2017-04-12 22:30 +0200
    Re: [patch 02/13] workqueue: Provide work_on_cpu_safe() Dou Liyang <douly.fnst@cn.fujitsu.com> - 2017-04-13 13:20 +0200
      Re: [patch 02/13] workqueue: Provide work_on_cpu_safe() Thomas Gleixner <tglx@linutronix.de> - 2017-04-13 23:30 +0200
    Re: [patch 02/13] workqueue: Provide work_on_cpu_safe() Tejun Heo <tj@kernel.org> - 2017-04-14 06:20 +0200
    Re: [patch 02/13] workqueue: Provide work_on_cpu_safe() Peter Zijlstra <peterz@infradead.org> - 2017-04-14 11:00 +0200
      Re: [patch 02/13] workqueue: Provide work_on_cpu_safe() Thomas Gleixner <tglx@linutronix.de> - 2017-04-14 12:00 +0200
        Re: [patch 02/13] workqueue: Provide work_on_cpu_safe() Peter Zijlstra <peterz@infradead.org> - 2017-04-14 12:00 +0200
    [tip:sched/core] workqueue: Provide work_on_cpu_safe() tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2017-04-15 16:30 +0200
  Re: [patch 00/13] sched/treewide: Clean up various racy task  affinity issues Peter Zijlstra <peterz@infradead.org> - 2017-04-13 11:10 +0200

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