Re: [tip:sched/core] sched: Fix hotplug vs. set_cpus_allowed_ptr()

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 05/22/2014 05:56 PM, tip-bot for Lai Jiangshan wrote:
> Commit-ID:  6acbfb96976fc3350e30d964acb1dbbdf876d55e
> Gitweb:     http://git.kernel.org/tip/6acbfb96976fc3350e30d964acb1dbbdf876d55e
> Author:     Lai Jiangshan <laijs@cn.fujitsu.com>
> AuthorDate: Fri, 16 May 2014 11:50:42 +0800
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Thu, 22 May 2014 10:21:31 +0200
> 
> sched: Fix hotplug vs. set_cpus_allowed_ptr()
> 
> Lai found that:
> 
>   WARNING: CPU: 1 PID: 13 at arch/x86/kernel/smp.c:124 native_smp_send_reschedule+0x2d/0x4b()
>   ...
>   migration_cpu_stop+0x1d/0x22
> 
> was caused by set_cpus_allowed_ptr() assuming that cpu_active_mask is
> always a sub-set of cpu_online_mask.
> 
> This isn't true since 5fbd036b552f ("sched: Cleanup cpu_active madness").
> 
> So set active and online at the same time to avoid this particular
> problem.
> 
> Fixes: 5fbd036b552f ("sched: Cleanup cpu_active madness")
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Michael wang <wangyun@linux.vnet.ibm.com>
> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Cc: Toshi Kani <toshi.kani@hp.com>
> Link: http://lkml.kernel.org/r/53758B12.8060609@cn.fujitsu.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

Regards,
Srivatsa S. Bhat

> ---
>  kernel/cpu.c        | 6 ++++--
>  kernel/sched/core.c | 1 -
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index a9e710e..247979a 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -726,10 +726,12 @@ void set_cpu_present(unsigned int cpu, bool present)
> 
>  void set_cpu_online(unsigned int cpu, bool online)
>  {
> -	if (online)
> +	if (online) {
>  		cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
> -	else
> +		cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
> +	} else {
>  		cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
> +	}
>  }
> 
>  void set_cpu_active(unsigned int cpu, bool active)
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 44e00ab..86f3890 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5076,7 +5076,6 @@ static int sched_cpu_active(struct notifier_block *nfb,
>  				      unsigned long action, void *hcpu)
>  {
>  	switch (action & ~CPU_TASKS_FROZEN) {
> -	case CPU_STARTING:
>  	case CPU_DOWN_FAILED:
>  		set_cpu_active((long)hcpu, true);
>  		return NOTIFY_OK;
>