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SubjectRe: [PATCH 02/13] blkcg: update blkg_lookup_create() to do locking
On Mon, Nov 26, 2018 at 04:19:35PM -0500, Dennis Zhou wrote:
> To know when to create a blkg, the general pattern is to do a
> blkg_lookup() and if that fails, lock and do the lookup again, and if
> that fails finally create. It doesn't make much sense for everyone who
> wants to do creation to write this themselves.
>
> This changes blkg_lookup_create() to do locking and implement this
> pattern. The old blkg_lookup_create() is renamed to
> __blkg_lookup_create(). If a call site wants to do its own error
> handling or already owns the queue lock, they can use
> __blkg_lookup_create(). This will be used in upcoming patches.
>
> Signed-off-by: Dennis Zhou <dennis@kernel.org>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> Acked-by: Tejun Heo <tj@kernel.org>
> Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
> ---
> block/blk-cgroup.c | 30 +++++++++++++++++++++++++++---
> block/blk-iolatency.c | 2 +-
> include/linux/blk-cgroup.h | 4 +++-
> 3 files changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 63d226a084cd..b1ec98eeeae0 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -249,7 +249,7 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
> }
>
> /**
> - * blkg_lookup_create - lookup blkg, try to create one if not there
> + * __blkg_lookup_create - lookup blkg, try to create one if not there
> * @blkcg: blkcg of interest
> * @q: request_queue of interest
> *
> @@ -262,8 +262,8 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
> * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not
> * dead and bypassing, returns ERR_PTR(-EBUSY).
> */
> -struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
> - struct request_queue *q)
> +struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg,
> + struct request_queue *q)
> {
> struct blkcg_gq *blkg;
>
> @@ -293,6 +293,30 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
> }
> }
>
> +/**
> + * blkg_lookup_create - find or create a blkg
> + * @blkcg: target block cgroup
> + * @q: target request_queue
> + *
> + * This looks up or creates the blkg representing the unique pair
> + * of the blkcg and the request_queue.
> + */
> +struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
> + struct request_queue *q)
> +{
> + struct blkcg_gq *blkg = blkg_lookup(blkcg, q);
> +
> + if (unlikely(!blkg)) {
> + spin_lock_irq(&q->queue_lock);
> +
> + blkg = __blkg_lookup_create(blkcg, q);
> +
> + spin_unlock_irq(&q->queue_lock);

No extra spaces here please, otherwise you can add

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

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