On 10/08/2015 05:35 PM, Kosuke Tatsukawa wrote: > btrfs_bio_counter_sub() seems to be missing a memory barrier which might > cause the waker to not notice the waiter and miss sending a wake_up as > in the following figure. > > btrfs_bio_counter_sub btrfs_rm_dev_replace_blocked > ------------------------------------------------------------------------ > if (waitqueue_active(&fs_info->replace_wait)) > /* The CPU might reorder the test for > the waitqueue up here, before > prior writes complete */ > /* wait_event */ > /* __wait_event */ > /* ___wait_event */ > long __int = prepare_to_wait_event(&wq, > &__wait, state); > if (!percpu_counter_sum(&fs_info->bio_counter)) > percpu_counter_sub(&fs_info->bio_counter, > amount); > schedule() percpu_counter_sub can't be reordered, in its most basic form it does preempt_disable/enable which in its most basic form does barrier(). Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
