Re: [linux-pm] Re: 2.6.21-rc7-mm2 suspend bug. [kernel/kthread.c]

[Gautham R Shenoy]

On Mon, Apr 30, 2007 at 12:39:46AM -0700, Andrew Morton wrote:
> On Sun, 29 Apr 2007 22:27:44 +0200 "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> 
> > On Sunday, 29 April 2007 21:51, Dan Kruchinin wrote:
> > > Hi all.
> > > 
> > > There is a problem on my macbook core duo with suspend.
> > > after suspending when i'm trying to 'wake up' my notebook, it seems
> > > that it works, but i don't see anything at my monitor. So i have to
> > > reboot it to continue my work.
> > 
> > What exactly do you do to suspend?
> > 
> 
> This is due to _cpu_down() calling kthread_bind() in state TASK_RUNNING.

The state should be TASK_INTERRUPTIBLE. That's the state of the thread
'p' should be in when we do a kthread_bind(p) in _cpu_down().

Are you sure about the TASK_RUNNING part ?

> 
> So I was sent the below, including worrisome changelog.
> 

Ok, it should not be that worrisome!
By the time we would be doing kthread_stop(p) in _cpu_down(), 'p' would have
been moved over to some other online cpu, due to the migrate_dead_tasks() 
called in CPU_DEAD handling of migration_call (kernel/sched.c).

So we are safe. Anyway, I apologise for causing any worry :-)

Thanks and Regards
gautham.
> 
> 
> 
> From: Gautham R Shenoy <ego@xxxxxxxxxx>
> 
> We are anyway kthread_stop()ping other per-cpu kernel threads after
> move_task_off_dead_cpu(), so we can do it with the stop_machine_run thread
> as well.
> 
> I just checked with Vatsa if there was any subtle reason why they
> had put in the kthread_bind() in cpu.c. Vatsa cannot seem to recollect
> any and I can't see any. So let us just remove the kthread_bind.
> 
> Signed-off-by: Gautham R Shenoy <ego@xxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
>  kernel/cpu.c |    4 ----
>  1 files changed, 4 deletions(-)
> 
> diff -puN kernel/cpu.c~remvoe-kthread_bind-call-from-_cpu_down kernel/cpu.c
> --- a/kernel/cpu.c~remvoe-kthread_bind-call-from-_cpu_down
> +++ a/kernel/cpu.c
> @@ -175,10 +175,6 @@ static int _cpu_down(unsigned int cpu)
>  	/* This actually kills the CPU. */
>  	__cpu_die(cpu);
> 
> -	/* Move it here so it can run. */
> -	kthread_bind(p, get_cpu());
> -	put_cpu();
> -
>  	/* CPU is completely dead: tell everyone.  Too late to complain. */
>  	if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD, hcpu) == NOTIFY_BAD)
>  		BUG();
> _
> 
> _______________________________________________
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-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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