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

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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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#1623574 — Re: [patch 02/13] workqueue: Provide work_on_cpu_safe()

On Wed, Apr 12, 2017 at 10:07:28PM +0200, Thomas Gleixner wrote:
> +long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
> +{
> +	long ret = -ENODEV;
> +
> +	get_online_cpus();
> +	if (cpu_online(cpu))
> +		ret = work_on_cpu(cpu, fn, arg);
> +	put_online_cpus();
> +	return ret;
> +}

But doesn't workqueue have this lovelt 'feature' where it will unbind
per-cpu work and run it on random CPUs when hotplug happens?

That is, I think you need a flush_work() before put_online_cpus() if you
want to guarantee anything.

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#1623626 — Re: [patch 02/13] workqueue: Provide work_on_cpu_safe()

On Fri, 14 Apr 2017, Peter Zijlstra wrote:

> On Wed, Apr 12, 2017 at 10:07:28PM +0200, Thomas Gleixner wrote:
> > +long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
> > +{
> > +	long ret = -ENODEV;
> > +
> > +	get_online_cpus();
> > +	if (cpu_online(cpu))
> > +		ret = work_on_cpu(cpu, fn, arg);
> > +	put_online_cpus();
> > +	return ret;
> > +}
> 
> But doesn't workqueue have this lovelt 'feature' where it will unbind
> per-cpu work and run it on random CPUs when hotplug happens?
> 
> That is, I think you need a flush_work() before put_online_cpus() if you
> want to guarantee anything.

work_on_cpu() is sychnronous, it flushes already.

Thanks,

	tglx

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#1623627 — Re: [patch 02/13] workqueue: Provide work_on_cpu_safe()

On Fri, Apr 14, 2017 at 11:51:07AM +0200, Thomas Gleixner wrote:
> On Fri, 14 Apr 2017, Peter Zijlstra wrote:
> 
> > On Wed, Apr 12, 2017 at 10:07:28PM +0200, Thomas Gleixner wrote:
> > > +long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
> > > +{
> > > +	long ret = -ENODEV;
> > > +
> > > +	get_online_cpus();
> > > +	if (cpu_online(cpu))
> > > +		ret = work_on_cpu(cpu, fn, arg);
> > > +	put_online_cpus();
> > > +	return ret;
> > > +}
> > 
> > But doesn't workqueue have this lovelt 'feature' where it will unbind
> > per-cpu work and run it on random CPUs when hotplug happens?
> > 
> > That is, I think you need a flush_work() before put_online_cpus() if you
> > want to guarantee anything.
> 
> work_on_cpu() is sychnronous, it flushes already.

So much for being awake ... 

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#1624071 — [tip:sched/core] workqueue: Provide work_on_cpu_safe()

Commit-ID:  0e8d6a9336b487a1dd6f1991ff376e669d4c87c6
Gitweb:     http://git.kernel.org/tip/0e8d6a9336b487a1dd6f1991ff376e669d4c87c6
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 12 Apr 2017 22:07:28 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 15 Apr 2017 12:20:53 +0200

workqueue: Provide work_on_cpu_safe()

work_on_cpu() is not protected against CPU hotplug. For code which requires
to be either executed on an online CPU or to fail if the CPU is not
available the callsite would have to protect against CPU hotplug.

Provide a function which does get/put_online_cpus() around the call to
work_on_cpu() and fails the call with -ENODEV if the target CPU is not
online.

Preparatory patch to convert several racy task affinity manipulations.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Len Brown <lenb@kernel.org>
Link: http://lkml.kernel.org/r/20170412201042.262610721@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 include/linux/workqueue.h |  5 +++++
 kernel/workqueue.c        | 23 +++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index bde063c..c102ef6 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -608,8 +608,13 @@ static inline long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
 {
 	return fn(arg);
 }
+static inline long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
+{
+	return fn(arg);
+}
 #else
 long work_on_cpu(int cpu, long (*fn)(void *), void *arg);
+long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg);
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_FREEZER
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c0168b7..5bf1be0 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4735,6 +4735,29 @@ long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
 	return wfc.ret;
 }
 EXPORT_SYMBOL_GPL(work_on_cpu);
+
+/**
+ * work_on_cpu_safe - run a function in thread context on a particular cpu
+ * @cpu: the cpu to run on
+ * @fn:  the function to run
+ * @arg: the function argument
+ *
+ * Disables CPU hotplug and calls work_on_cpu(). The caller must not hold
+ * any locks which would prevent @fn from completing.
+ *
+ * Return: The value @fn returns.
+ */
+long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
+{
+	long ret = -ENODEV;
+
+	get_online_cpus();
+	if (cpu_online(cpu))
+		ret = work_on_cpu(cpu, fn, arg);
+	put_online_cpus();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(work_on_cpu_safe);
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_FREEZER

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#1622836 — Re: [patch 00/13] sched/treewide: Clean up various racy task affinity issues

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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