Messages in this thread | | | Date | Wed, 7 May 2014 20:06:21 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] [RFC] perf: Fix a race between ring_buffer_detach() and ring_buffer_wakeup() |
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On Wed, May 07, 2014 at 02:35:26PM +0200, Peter Zijlstra wrote: > static void ring_buffer_attach(struct perf_event *event, > struct ring_buffer *rb) > { > + struct ring_buffer *old_rb = NULL; > unsigned long flags; > > + if (event->rb) { > + /* > + * Should be impossible, we set this when removing > + * event->rb_entry and wait/clear when adding event->rb_entry. > + */ > + WARN_ON_ONCE(event->rcu_pending); > > + old_rb = event->rb; > + event->rcu_batches = get_state_synchronize_rcu(); > + event->rcu_pending = 1; > > + spin_lock_irqsave(&rb->event_lock, flags); > + list_del_rcu(&event->rb_entry); > + spin_unlock_irqrestore(&rb->event_lock, flags);
This all works a whole lot better if you make that old_rb->event_lock.
> + } > > + if (event->rcu_pending && rb) { > + cond_synchronize_rcu(event->rcu_batches); > + event->rcu_pending = 0; > + } > > + if (rb) { > + spin_lock_irqsave(&rb->event_lock, flags); > + list_add_rcu(&event->rb_entry, &rb->event_list); > + spin_unlock_irqrestore(&rb->event_lock, flags); > + } > + > + rcu_assign_pointer(event->rb, rb); > + > + if (old_rb) { > + ring_buffer_put(old_rb); > + /* > + * Since we detached before setting the new rb, so that we > + * could attach the new rb, we could have missed a wakeup. > + * Provide it now. > + */ > + wake_up_all(&event->waitq); > + } > } [unhandled content-type:application/pgp-signature] | |