Re: -next: Nov 12 - kernel BUG at kernel/sched.c:7359!

[Sachin Sant <sachinp@in.ibm.com>]

Peter Zijlstra wrote:
> Correct, Ingo objected to the fastpath overhead.
>
> Could you please try the below patch which tries to address the issue
> differently.
>   
Works great. Thanks

Tested-by: Sachin Sant <sachinp@in.ibm.com>

Regards
-Sachin

> ---
> Subject: sched: Fix balance vs hotplug race
> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date: Wed Nov 25 13:31:39 CET 2009
>
> Since (e761b77: cpu hotplug, sched: Introduce cpu_active_map and redo
> sched domain managment) we have cpu_active_mask which is suppose to
> rule scheduler migration and load-balancing, except it never did.
>
> The particular problem being solved here is a crash in
> try_to_wake_up() where select_task_rq() ends up selecting an offline
> cpu because select_task_rq_fair() trusts the sched_domain tree to reflect
> the current state of affairs, similarly select_task_rq_rt() trusts the
> root_domain.
>
> However, the sched_domains are updated from CPU_DEAD, which is after
> the cpu is taken offline and after stop_machine is done. Therefore it
> can race perfectly well with code assuming the domains are right.
>
> Cure this by building the domains from cpu_active_mask on
> CPU_DOWN_PREPARE.
>
>   


-- 

---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
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