Messages in this thread |  | | Date | Fri, 27 Feb 2015 10:52:40 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/1] futex: don't spin waiting for PF_EXITING -> PF_EXITPIDONE transition |
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On Mon, Feb 16, 2015 at 09:13:36PM +0100, Oleg Nesterov wrote:
> diff --git a/kernel/futex.c b/kernel/futex.c > index b101381..c1104a8 100644 > +++ b/kernel/futex.c > @@ -716,11 +716,13 @@ void exit_pi_state_list(struct task_struct *curr) > > if (!futex_cmpxchg_enabled) > return; > + > /* > + * attach_to_pi_owner() can no longer add the new entry. But > + * we have to be careful versus waiters unqueueing themselves. > */ > + curr->flags |= PF_EXITPIDONE; > + > raw_spin_lock_irq(&curr->pi_lock); > while (!list_empty(head)) { >
Should we not set PF_EXITPIDONE _inside_ the pi_lock? To properly serialize against the below check?
> @@ -905,24 +907,12 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key, > return -EPERM; > } > > raw_spin_lock_irq(&p->pi_lock); > + if (unlikely(p->flags & PF_EXITPIDONE)) { > + /* exit_pi_state_list() was already called */ > raw_spin_unlock_irq(&p->pi_lock); > put_task_struct(p); > + return -ESRCH; > } > > /*
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