[Devel] [PATCH rh7 1/2] cfq-iosched: don't call wbt_disable_default() with IRQs disabled

[Pavel Tikhomirov]

Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

On 10/30/19 1:32 PM, Andrey Ryabinin wrote:
> From: Jens Axboe <axboe at fb.com>
> 
> wbt_disable_default() calls del_timer_sync() to wait for the wbt
> timer to finish before disabling throttling. We can't do this with
> IRQs disable. This fixes a lockdep splat on boot, if non-root
> cgroups are used.
> 
> Reported-by: Gabriel C <nix.or.die at gmail.com>
> Fixes: 87760e5eef35 ("block: hook up writeback throttling")
> Signed-off-by: Jens Axboe <axboe at fb.com>
> (cherry picked from commit 5d7f5ce15156af205e175e8fa5c669ba40bf0c5e)
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
> ---
>   block/cfq-iosched.c | 25 +++++++++++++------------
>   1 file changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 1af4377ba938..350e9d740b60 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -3614,7 +3614,7 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>   }
>   
>   #ifdef CONFIG_CFQ_GROUP_IOSCHED
> -static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
> +static bool check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
>   {
>   	struct cfq_data *cfqd = cic_to_cfqd(cic);
>   	struct cfq_queue *sync_cfqq;
> @@ -3631,15 +3631,7 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
>   	 * spuriously on a newly created cic but there's no harm.
>   	 */
>   	if (unlikely(!cfqd) || likely(cic->blkcg_id == id))
> -		return;
> -
> -	/*
> -	 * If we have a non-root cgroup, we can depend on that to
> -	 * do proper throttling of writes. Turn off wbt for that
> -	 * case, if it was enabled by default.
> -	 */
> -	if (nonroot_cg)
> -		wbt_disable_default(cfqd->queue);
> +		return nonroot_cg;
>   
>   	sync_cfqq = cic_to_cfqq(cic, 1);
>   	if (sync_cfqq) {
> @@ -3653,9 +3645,13 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
>   	}
>   
>   	cic->blkcg_id = id;
> +	return nonroot_cg;
>   }
>   #else
> -static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
> +static inline bool check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
> +{
> +	return false;
> +}
>   #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
>   
>   static struct cfq_queue *
> @@ -4282,11 +4278,12 @@ cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
>   	const int rw = rq_data_dir(rq);
>   	const bool is_sync = rq_is_sync(rq);
>   	struct cfq_queue *cfqq;
> +	bool disable_wbt;
>   
>   	spin_lock_irq(q->queue_lock);
>   
>   	check_ioprio_changed(cic, bio);
> -	check_blkcg_changed(cic, bio);
> +	disable_wbt = check_blkcg_changed(cic, bio);
>   new_queue:
>   	cfqq = cic_to_cfqq(cic, is_sync);
>   	if (!cfqq || cfqq == &cfqd->oom_cfqq) {
> @@ -4322,6 +4319,10 @@ cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
>   	rq->elv.priv[0] = cfqq;
>   	rq->elv.priv[1] = cfqq->cfqg;
>   	spin_unlock_irq(q->queue_lock);
> +
> +	if (disable_wbt)
> +		wbt_disable_default(q);
> +
>   	return 0;
>   }
>   
> 

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.