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SubjectRe: [PATCH -tip v2] sched: more sched_domain iterations fix
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On Fri, 2011-04-22 at 18:53 +0800, Xiaotian feng wrote:
> From: Xiaotian Feng <dfeng@redhat.com>
>
> sched_domain iterations needs to be protected by rcu_read_lock() now,
> this patch adds another two places which needs the rcu lock, which is
> spotted by following suspicious rcu_dereference_check() usage warnings.
>
> kernel/sched_rt.c:1244 invoked rcu_dereference_check() without protection!
> kernel/sched_stats.h:41 invoked rcu_dereference_check() without protection!

Much better, one worry:

> Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Peter Zijlstra <peterz@infradead.org>
> ---

> diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
> index 48ddf43..331e01b 100644
> --- a/kernel/sched_stats.h
> +++ b/kernel/sched_stats.h
> @@ -37,7 +37,7 @@ static int show_schedstat(struct seq_file *seq, void *v)
>
> #ifdef CONFIG_SMP
> /* domain-specific stats */
> - preempt_disable();
> + rcu_read_lock();
> for_each_domain(cpu, sd) {
> enum cpu_idle_type itype;
>
> @@ -64,7 +64,7 @@ static int show_schedstat(struct seq_file *seq, void *v)
> sd->ttwu_wake_remote, sd->ttwu_move_affine,
> sd->ttwu_move_balance);
> }
> - preempt_enable();
> + rcu_read_unlock();
> #endif
> }
> kfree(mask_str);

Did you indeed validate that the preempt_disable() wasn't needed for
anything else? Your changelog doesn't mention and I didn't check, just
noticed the possibility on the first posting.


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