Messages in this thread | | | Subject | Re: [PATCH] sched: fix tsk->pi_lock isn't held when do_set_cpus_allowed() | From | Wanpeng Li <> | Date | Tue, 25 Aug 2015 18:18:36 +0800 |
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On 8/25/15 6:05 PM, Peter Zijlstra wrote: > On Tue, Aug 25, 2015 at 03:59:54PM +0800, Wanpeng Li wrote: >> +++ b/kernel/cpuset.c >> @@ -2376,8 +2376,12 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) >> >> void cpuset_cpus_allowed_fallback(struct task_struct *tsk) >> { >> + unsigned long flags; >> + >> rcu_read_lock(); >> + raw_spin_lock_irqsave(&tsk->pi_lock, flags); >> do_set_cpus_allowed(tsk, task_cs(tsk)->effective_cpus); >> + raw_spin_lock_irqsave(&tsk->pi_lock, flags); >> rcu_read_unlock(); > Aside from the double lock thing that was already pointed out, I think > this is wrong, because the select_task_rq() call can already have > pi_lock held. > > Taking it again would result in a deadlock. > > Consider for instance: > > try_to_wake_up() > raw_spin_lock_irqsave(->pi_lock) > select_task_rq() > select_ballback_rq() > cpuset_cpus_allowed_fallback() > raw_spin_lock_irqsave(->pi_lock) > > > The problem is with the migration path and should be fixed there.
Indeed, it should be fixed in migration path. I will try to fight it out and post a patch. :)
Regards, Wanpeng Li
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