В Пн, 20/10/2014 в 11:13 +0200, Peter Zijlstra пишет:
> OK, I think I'm finally awake enough to see what you're all talking
> about :-)
>
> On Sun, Oct 19, 2014 at 09:37:44PM +0200, Oleg Nesterov wrote:
> > > > RT tree has:
> > > >
> > > > https://git.kernel.org/cgit/linux/kernel/git/paulg/3.10-rt
OK, I think I'm finally awake enough to see what you're all talking
about :-)
On Sun, Oct 19, 2014 at 09:37:44PM +0200, Oleg Nesterov wrote:
> > > RT tree has:
> > >
> > > https://git.kernel.org/cgit/linux/kernel/git/paulg/3.10-rt-patches.git/
> > > tree/patches/sched-delay-put-task.patch
(answe
В Вс, 19/10/2014 в 21:43 +0200, Oleg Nesterov пишет:
> On 10/19, Oleg Nesterov wrote:
> >
> > Forgot to mention... Or we can make task_struct_cachep SLAB_DESTROY_BY_RCU,
> > in this case ->curr (or any other "task_struct *" ponter) can not go away
> > under rcu_read_lock(). task_numa_compare() stil
В Вс, 19/10/2014 в 21:24 +0200, Oleg Nesterov пишет:
> On 10/19, Kirill Tkhai wrote:
> >
> > 19.10.2014, 00:59, "Oleg Nesterov" :
> >
> > > No, I don't think this can work. Let's look at the current code:
> > >
> > > rcu_read_lock();
> > > cur = ACCESS_ONCE(dst_rq->curr);
> > >
В Вс, 19/10/2014 в 23:38 +0200, Peter Zijlstra пишет:
> On Sun, Oct 19, 2014 at 03:13:31AM +0400, Kirill Tkhai wrote:
>
> I'm too tired for all this, but:
>
> > + smp_rmb(); /* Pairs with dst_rq->lock unlocking which implies smp_wmb */
>
> RELEASE does not imply a WMB.
Thanks, please see, I'v
On Sun, Oct 19, 2014 at 03:13:31AM +0400, Kirill Tkhai wrote:
I'm too tired for all this, but:
> + smp_rmb(); /* Pairs with dst_rq->lock unlocking which implies smp_wmb */
RELEASE does not imply a WMB.
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On 10/19, Oleg Nesterov wrote:
>
> Forgot to mention... Or we can make task_struct_cachep SLAB_DESTROY_BY_RCU,
> in this case ->curr (or any other "task_struct *" ponter) can not go away
> under rcu_read_lock(). task_numa_compare() still needs the PF_EXITING check,
> but we do not need to recheck -
On 10/19, Oleg Nesterov wrote:
>
> On 10/19, Kirill Tkhai wrote:
> >
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1165,7 +1165,30 @@ static void task_numa_compare(struct task_numa_env
> > *env,
> >
> > rcu_read_lock();
> > cur = ACCESS_ONCE(dst_rq->curr);
> > - if
On 10/19, Kirill Tkhai wrote:
>
> 19.10.2014, 00:59, "Oleg Nesterov" :
>
> > No, I don't think this can work. Let's look at the current code:
> >
> > rcu_read_lock();
> > cur = ACCESS_ONCE(dst_rq->curr);
> > if (cur->pid == 0) /* idle */
> >
> > And any dereference, eve
On 18.10.2014 23:36, Peter Zijlstra wrote:
> On Sat, Oct 18, 2014 at 12:33:27PM +0400, Kirill Tkhai wrote:
>> How about this?
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index b78280c..d46427e 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1165,7 +1165,2
19.10.2014, 00:59, "Oleg Nesterov" :
> On 10/18, Kirill Tkhai wrote:
>> 18.10.2014, 01:40, "Oleg Nesterov" :
>>> ...
>>> The
>>> task_struct itself can't go away,
>>> ...
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -1158,7 +1158,13 @@ static void task_numa_co
On 10/18, Peter Zijlstra wrote:
>
> So you worry about the refcount doing 0->1 ? In which case the above is
> still wrong and we should be using atomic_inc_not_zero() in order to
> acquire the reference count.
It is actually worse, please see my reply to Kirill. We simply can't
dereference foreign
On 10/18, Kirill Tkhai wrote:
>
> 18.10.2014, 01:40, "Oleg Nesterov" :
> > ...
> > The
> > task_struct itself can't go away,
> > ...
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1158,7 +1158,13 @@ static void task_numa_compare(struct task_numa_env
> > *env,
> >
> >
On Sat, Oct 18, 2014 at 12:33:27PM +0400, Kirill Tkhai wrote:
> How about this?
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b78280c..d46427e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1165,7 +1165,21 @@ static void task_numa_compare(struct task_numa
And smp_rmb() beetween ifs which is pairs with rq unlocking
> 18.10.2014, 12:15, "Kirill Tkhai" :
>
>> 18.10.2014, 01:40, "Oleg Nesterov" :
>>
>>> The lockless get_task_struct(tsk) is only safe if tsk == current
>>> and didn't pass exit_notify(), or if this tsk was found on a rcu
>>> protected li
18.10.2014, 12:15, "Kirill Tkhai" :
> 18.10.2014, 01:40, "Oleg Nesterov" :
>> The lockless get_task_struct(tsk) is only safe if tsk == current
>> and didn't pass exit_notify(), or if this tsk was found on a rcu
>> protected list (say, for_each_process() or find_task_by_vpid()).
>> IOW, it is on
18.10.2014, 01:40, "Oleg Nesterov" :
> The lockless get_task_struct(tsk) is only safe if tsk == current
> and didn't pass exit_notify(), or if this tsk was found on a rcu
> protected list (say, for_each_process() or find_task_by_vpid()).
> IOW, it is only safe if release_task() was not called befor
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