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    Subject[tip:sched/core] sched: Fix sched_domain iterations vs. RCU
    Commit-ID:  057f3fadb347e9c51b07e1b277bbdda79f976768
    Gitweb: http://git.kernel.org/tip/057f3fadb347e9c51b07e1b277bbdda79f976768
    Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    AuthorDate: Mon, 18 Apr 2011 11:24:34 +0200
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Tue, 19 Apr 2011 10:56:54 +0200

    sched: Fix sched_domain iterations vs. RCU

    Vladis Kletnieks reported a new RCU debug warning in the scheduler.

    Since commit dce840a08702b ("sched: Dynamically allocate sched_domain/
    sched_group data-structures") the sched_domain trees are protected by
    RCU instead of RCU-sched.

    This means that we need to include rcu_read_lock() protection when we
    iterate them since disabling preemption doesn't suffice anymore.

    Reported-by: Valdis.Kletnieks@vt.edu
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/1302882741.2388.241.camel@twins
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/sched.c | 14 +++++++++++---
    1 files changed, 11 insertions(+), 3 deletions(-)

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 0cfe031..27d3e73 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -1208,11 +1208,17 @@ int get_nohz_timer_target(void)
    int i;
    struct sched_domain *sd;

    + rcu_read_lock();
    for_each_domain(cpu, sd) {
    - for_each_cpu(i, sched_domain_span(sd))
    - if (!idle_cpu(i))
    - return i;
    + for_each_cpu(i, sched_domain_span(sd)) {
    + if (!idle_cpu(i)) {
    + cpu = i;
    + goto unlock;
    + }
    + }
    }
    +unlock:
    + rcu_read_unlock();
    return cpu;
    }
    /*
    @@ -2415,12 +2421,14 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
    struct sched_domain *sd;

    schedstat_inc(p, se.statistics.nr_wakeups_remote);
    + rcu_read_lock();
    for_each_domain(this_cpu, sd) {
    if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
    schedstat_inc(sd, ttwu_wake_remote);
    break;
    }
    }
    + rcu_read_unlock();
    }
    #endif /* CONFIG_SMP */


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