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sched: Fix set_cpu_active() in cpu_down()

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Sachin found cpu hotplug test failures on powerpc, which made
the kernel hang on his POWER box.

The problem is that we fail to re-activate a cpu when a
hot-unplug fails. Fix this by moving the de-activation into
_cpu_down after doing the initial checks.

Remove the synchronize_sched() calls and rely on those implied
by rebuilding the sched domains using the new mask.

Reported-by: Sachin Sant <sachinp@in.ibm.com>
Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
Tested-by: Sachin Sant <sachinp@in.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091216170517.500272612@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Xiaotian Feng 2009-12-16 18:04:32 +01:00 committed by Ingo Molnar
parent 933b0618d8
commit 9ee349ad6d
1 changed files with 3 additions and 21 deletions
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24
kernel/cpu.c
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@ -209,6 +209,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
return -ENOMEM; return -ENOMEM;
cpu_hotplug_begin(); cpu_hotplug_begin();
set_cpu_active(cpu, false);
err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
hcpu, -1, &nr_calls); hcpu, -1, &nr_calls);
if (err == NOTIFY_BAD) { if (err == NOTIFY_BAD) {
@ -280,18 +281,6 @@ int __ref cpu_down(unsigned int cpu)
goto out; goto out;
} }
set_cpu_active(cpu, false);
/*
* Make sure the all cpus did the reschedule and are not
* using stale version of the cpu_active_mask.
* This is not strictly necessary becuase stop_machine()
* that we run down the line already provides the required
* synchronization. But it's really a side effect and we do not
* want to depend on the innards of the stop_machine here.
*/
synchronize_sched();
err = _cpu_down(cpu, 0); err = _cpu_down(cpu, 0);
out: out:
@ -382,19 +371,12 @@ int disable_nonboot_cpus(void)
return error; return error;
cpu_maps_update_begin(); cpu_maps_update_begin();
first_cpu = cpumask_first(cpu_online_mask); first_cpu = cpumask_first(cpu_online_mask);
/* We take down all of the non-boot CPUs in one shot to avoid races /*
* We take down all of the non-boot CPUs in one shot to avoid races
* with the userspace trying to use the CPU hotplug at the same time * with the userspace trying to use the CPU hotplug at the same time
*/ */
cpumask_clear(frozen_cpus); cpumask_clear(frozen_cpus);
for_each_online_cpu(cpu) {
if (cpu == first_cpu)
continue;
set_cpu_active(cpu, false);
}
synchronize_sched();
printk("Disabling non-boot CPUs ...\n"); printk("Disabling non-boot CPUs ...\n");
for_each_online_cpu(cpu) { for_each_online_cpu(cpu) {
if (cpu == first_cpu) if (cpu == first_cpu)