On Tue, Apr 18, 2017 at 04:29:42PM -0700, Bart Van Assche wrote:
> A later patch in this series will modify blk_mq_debugfs_register()
> such that it uses q->kobj.parent to determine the name of a
> request queue. Hence make sure that that pointer is initialized
> before blk_mq_debugfs_register() is called. To avoid lock inversion,
> protect sysfs / debugfs registration with the queue sysfs_lock
> instead of the global mutex all_q_mutex.
I think this is sane, I don't see why we would need all_q_mutex for
this. One comment below, however.
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Cc: Omar Sandoval <osandov@xxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> ---
> block/blk-mq-sysfs.c | 43 +++++++++++++++++++++++++++++++++++--------
> block/blk-mq.h | 1 +
> block/blk-sysfs.c | 6 +++---
> 3 files changed, 39 insertions(+), 11 deletions(-)
>
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index d745ab81033a..54ef9402914c 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/block/blk-mq-sysfs.c
> @@ -253,6 +253,8 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
> struct blk_mq_hw_ctx *hctx;
> int i;
>
> + lockdep_assert_held(&q->sysfs_lock);
> +
> queue_for_each_hw_ctx(q, hctx, i)
> blk_mq_unregister_hctx(hctx);
>
> @@ -267,9 +269,9 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
>
> void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
> {
> - blk_mq_disable_hotplug();
> + mutex_lock(&q->sysfs_lock);
> __blk_mq_unregister_dev(dev, q);
> - blk_mq_enable_hotplug();
> + mutex_unlock(&q->sysfs_lock);
> }
>
> void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx)
> @@ -302,12 +304,13 @@ void blk_mq_sysfs_init(struct request_queue *q)
> }
> }
>
> -int blk_mq_register_dev(struct device *dev, struct request_queue *q)
> +int __blk_mq_register_dev(struct device *dev, struct request_queue *q)
> {
> struct blk_mq_hw_ctx *hctx;
> int ret, i;
>
> - blk_mq_disable_hotplug();
> + WARN_ON_ONCE(!q->kobj.parent);
> + lockdep_assert_held(&q->sysfs_lock);
>
> ret = kobject_add(&q->mq_kobj, kobject_get(&dev->kobj), "%s", "mq");
> if (ret < 0)
> @@ -327,8 +330,20 @@ int blk_mq_register_dev(struct device *dev, struct request_queue *q)
> __blk_mq_unregister_dev(dev, q);
> else
> q->mq_sysfs_init_done = true;
> +
> out:
> - blk_mq_enable_hotplug();
> + return ret;
> +}
> +
> +int blk_mq_register_dev(struct device *dev, struct request_queue *q)
> +{
> + int ret;
> +
> + ret = mutex_lock_interruptible(&q->sysfs_lock);
Why did you make this interruptible? blk_mq_disable_hotplug() wasn't
interruptible before, so now dm_mq_init_request_queue() can fail
silently if it is interrupted.
