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    SubjectRe: [PATCH -tip] sched: more sched_domain iterations fix
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    On Thu, 2011-04-21 at 19:07 +0800, Xiaotian Feng wrote:
    > sched_domain iterations needs to be protected by rcu_read_lock() now,
    > this patch adds another two places which needs the rcu lock.

    Changelog fails to mention how you found out about these.

    > Signed-off-by: Xiaotian Feng <dfeng@redhat.com>
    > Cc: Ingo Molnar <mingo@elte.hu>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > ---
    > kernel/sched_rt.c | 2 ++
    > kernel/sched_stats.h | 2 ++
    > 2 files changed, 4 insertions(+), 0 deletions(-)
    >
    > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
    > index 19ecb31..901ed2a 100644
    > --- a/kernel/sched_rt.c
    > +++ b/kernel/sched_rt.c
    > @@ -1282,7 +1282,9 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
    > int cpu;
    >
    > for (tries = 0; tries < RT_MAX_TRIES; tries++) {
    > + rcu_read_lock();
    > cpu = find_lowest_rq(task);
    > + rcu_read_unlock();

    I would put that inside find_lowest_rq() instead of around.

    > if ((cpu == -1) || (cpu == rq->cpu))
    > break;
    > diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
    > index 48ddf43..d25c8c1 100644
    > --- a/kernel/sched_stats.h
    > +++ b/kernel/sched_stats.h
    > @@ -38,6 +38,7 @@ 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;
    >
    > @@ -64,6 +65,7 @@ static int show_schedstat(struct seq_file *seq, void *v)
    > sd->ttwu_wake_remote, sd->ttwu_move_affine,
    > sd->ttwu_move_balance);
    > }
    > + rcu_read_unlock();
    > preempt_enable();

    I suspect that those preempt_disable/enable are an attempt at
    rcu_read_lock_sched() before that existed, which would suggest they are
    now redundant.

    > #endif
    > }





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