On 8.03.2018 13:49, David Sterba wrote:
> Add convenience wrappers for the waitqueue management that involves
> memory barriers to prevent deadlocks. The helpers will let us remove
> barriers and the necessary comments in several places.
>
> Signed-off-by: David Sterba <dste...@suse.com>
Reviewed-by: Nikolay Borisov <nbori...@suse.com>
> ---
> fs/btrfs/ctree.h | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index bf545e7552b8..c9827a1b676d 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3748,4 +3748,27 @@ static inline int btrfs_is_testing(struct
> btrfs_fs_info *fs_info)
> #endif
> return 0;
> }
> +
> +static inline void cond_wake_up(struct wait_queue_head *wq)
> +{
> + /*
> + * This implies a full smp_mb barrier, see comments for
> + * waitqueue_active why.
> + */
> + if (wq_has_sleeper(wq))
> + wake_up(wq);
> +}
> +
> +static inline void cond_wake_up_nomb(struct wait_queue_head *wq)
> +{
> + /*
> + * Special case for conditional wakeup where the barrier required for
> + * waitqueue_active is implied by some of the preceding code. Eg. one
> + * of such atomic operations (atomic_dec_and_return, ...), or a
> + * unlock/lock sequence, etc.
> + */
> + if (waitqueue_active(wq))
> + wake_up(wq);
> +}
> +
> #endif
>
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