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    SubjectRe: [PATCH v4] sched/numa: fix unsafe get_task_struct() in task_numa_assign()
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    В Пн, 10/11/2014 в 19:10 +0300, Kirill Tkhai пишет:
    > В Пн, 10/11/2014 в 17:03 +0100, Peter Zijlstra пишет:
    > > On Fri, Nov 07, 2014 at 10:48:27PM -0500, Sasha Levin wrote:
    > > > [ 829.539183] BUG: spinlock recursion on CPU#10, trinity-c594/11067
    > > > [ 829.539203] lock: 0xffff880631dd6b80, .magic: dead4ead, .owner: trinity-c594/11067, .owner_cpu: 13
    > >
    > > Ooh, look at that. CPU#10 vs .owner_cpu: 13 on the _same_ task.
    > >
    > > One of those again :/
    >
    > We do not initialyse task_struct::numa_preferred_nid for INIT_TASK.
    > It there no a problem?
    >

    I mean task_numa_find_cpu(). If a garbage is in cpumask_of_node(env->dst_nid)
    and cpu is bigger than mask, the check

    cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)

    may be true.

    So, we dereference wrong rq in task_numa_compare(). It's not rq at all.
    Strange cpu may be from here. It's just a int number in a wrong memory.

    A hypothesis that below may help:

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 826fdf3..a2b4a8a 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -1376,6 +1376,9 @@ static void task_numa_find_cpu(struct task_numa_env *env,
    {
    int cpu;

    + if (!node_online(env->dst_nid))
    + return;
    +
    for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
    /* Skip this CPU if the source task cannot migrate */
    if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)))



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