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SubjectRe: Regression in 2.6.27-rc1 for set_cpus_allowed_ptr

* Dmitry Adamushko <dmitry.adamushko@gmail.com> wrote:

> 2008/8/8 Rafael J. Wysocki <rjw@sisk.pl>:
> > [Adding CCs]
> >
> > On Friday, 8 of August 2008, Langsdorf, Mark wrote:
> >> One of my co-workers noticed that the powernow-k8
> >> driver no longer restarts when a CPU core is
> >> hot-disabled and then hot-enabled on AMD quad-core
> >> systems.
> >>
> >> The following comands work fine on 2.6.26 and fail
> >> on 2.6.27-rc1:
> >>
> >> echo 0 > /sys/devices/system/cpu/cpu3/online
> >> echo 1 > /sys/devices/system/cpu/cpu3/online
> >> find /sys -name cpufreq
> >>
> >> For 2.6.26, the find will return a cpufreq
> >> directory for each processor. In 2.6.27-rc1,
> >> the cpu3 directory is missing.
> >>
> >> After digging through the code, the following
> >> logic is failing when the core is hot-enabled
> >> at runtime. The code works during the boot
> >> sequence.
> >>
> >> cpumask_t = current->cpus_allowed;
> >> set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu));
> >> if (smp_processor_id() != cpu)
> >> return -ENODEV;
> >>
>
>
> if it gets called from any of the cpu-hotplug handlers, it won't work
> now (x86-microcode is another victim).
>
> Please give a try to the following patch: http://lkml.org/lkml/2008/7/30/171
>
> does it help?
>
> (the explanation is also available in this thread).

i've queued up the fix below in tip/sched/urgent.

Ingo

------------------------>
From 3bc8fb8f85b79aa2d6341adb5090799b93d64bc9 Mon Sep 17 00:00:00 2001
From: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Date: Wed, 30 Jul 2008 12:34:04 +0200
Subject: [PATCH] sched, cpu hotplug: fix set_cpus_allowed() use in hotplug callbacks

Mark Langsdorf reported:

> One of my co-workers noticed that the powernow-k8
> driver no longer restarts when a CPU core is
> hot-disabled and then hot-enabled on AMD quad-core
> systems.
>
> The following comands work fine on 2.6.26 and fail
> on 2.6.27-rc1:
>
> echo 0 > /sys/devices/system/cpu/cpu3/online
> echo 1 > /sys/devices/system/cpu/cpu3/online
> find /sys -name cpufreq
>
> For 2.6.26, the find will return a cpufreq
> directory for each processor. In 2.6.27-rc1,
> the cpu3 directory is missing.
>
> After digging through the code, the following
> logic is failing when the core is hot-enabled
> at runtime. The code works during the boot
> sequence.
>
> cpumask_t = current->cpus_allowed;
> set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu));
> if (smp_processor_id() != cpu)
> return -ENODEV;

a similar problem also affects the microcode driver.

So set the CPU active before calling the CPU_ONLINE notifier chain,
there are a handful of notifiers that use set_cpus_allowed().

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/cpu.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index e202a68..c977c33 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -349,6 +349,8 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
goto out_notify;
BUG_ON(!cpu_online(cpu));

+ cpu_set(cpu, cpu_active_map);
+
/* Now call notifier in preparation. */
raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);

@@ -383,9 +385,6 @@ int __cpuinit cpu_up(unsigned int cpu)

err = _cpu_up(cpu, 0);

- if (cpu_online(cpu))
- cpu_set(cpu, cpu_active_map);
-
out:
cpu_maps_update_done();
return err;

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