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    SubjectRe: [PATCH V4 1/2] sched/fair: Fix load_balance() affinity redo path
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    On 6/2/2017 4:27 PM, Jeffrey Hugo wrote:
    >
    > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    > index d711093..84255ab 100644
    > --- a/kernel/sched/fair.c
    > +++ b/kernel/sched/fair.c
    > @@ -6737,10 +6737,10 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
    > * our sched_group. We may want to revisit it if we couldn't
    > * meet load balance goals by pulling other tasks on src_cpu.
    > *
    > - * Also avoid computing new_dst_cpu if we have already computed
    > - * one in current iteration.
    > + * Avoid computing new_dst_cpu for NEWLY_IDLE or if we have
    > + * already computed one in current iteration.
    > */
    > - if (!env->dst_grpmask || (env->flags & LBF_DST_PINNED))
    > + if (env->idle == CPU_NEWLY_IDLE || (env->flags & LBF_DST_PINNED))
    > return 0;

    Self NACK. This breaks active_load_balance_cpu_stop(). Looks like
    env->idle == CPU_IDLE, but env->dst_grpmask is uninitialized, so it can
    be NULL, which causes a null pointer dereference a few lines later.

    I'm still having a look to see what makes sense to address the issue.


    --
    Jeffrey Hugo
    Qualcomm Datacenter Technologies as an affiliate of Qualcomm
    Technologies, Inc.
    Qualcomm Technologies, Inc. is a member of the
    Code Aurora Forum, a Linux Foundation Collaborative Project.

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