Hi Wanpeng,
On Fri, Aug 28, 2015 at 12:02:47PM +0800, Wanpeng Li wrote:
<snip>
> This patch fix it by following the rules for changing
> task_struct::cpus_allowed
> w/ both pi_lock and rq->lock are held.
>
> Reported-by: kernel test robot <ying.hu...@intel.com>
> Reported-by: Sasha Levin <sasha.le...@oracle.com>
> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
> ---
> v1 -> v2:
> * fix the silly double lock stuff
> * follow the rules for changing task_struct::cpus_allowed
>
> kernel/sched/core.c | 22 ++++++++++++++++++++++
> 1 files changed, 22 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b3386c6..8cf87e3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5186,6 +5186,27 @@ static void migrate_tasks(struct rq *dead_rq)
> BUG_ON(!next);
> next->sched_class->put_prev_task(rq, next);
>
> + /*
> + * Rules for changing task_struct::cpus_allowed are holding
> + * both pi_lock and rq->lock, such that holding either
> + * stabilizes the mask.
> + *
> + * Drop rq->lock is not quite as disastrous as it usually is
> + * because !cpu_active at this point, which means load-balance
> + * will not interfere.
> + */
> + lockdep_unpin_lock(&rq->lock);
> + raw_spin_unlock(&rq->lock);
> + raw_spin_lock(&next->pi_lock);
> + raw_spin_lock(&rq->lock);
> + lockdep_pin_lock(&rq->lock);
> + if (!(task_rq(next) == rq && task_on_rq_queued(next))) {
> + lockdep_unpin_lock(&rq->lock);
> + raw_spin_unlock(&rq->lock);Dropping rq->lock here means we will continue the loop without the rq->lock, right? But we do have a lockdep_pin_lock(&rq->lock) in the beginning of every iteration. So can we release rq->lock here? Regards, Boqun > + raw_spin_unlock(&next->pi_lock); > + continue; > + } > + > /* Find suitable destination for @next, with force if needed. */ > dest_cpu = select_fallback_rq(dead_rq->cpu, next); > > @@ -5196,6 +5217,7 @@ static void migrate_tasks(struct rq *dead_rq) > rq = dead_rq; > raw_spin_lock(&rq->lock); > } > + raw_spin_unlock(&next->pi_lock); > } > > rq->stop = stop; > -- > 1.7.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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