Re: [PATCH v6 2/2] block: cancel all throttled bios in del_gendisk()

Ming Lei
2022-01-12T03:06:36Z

Hello Yu Kuai,

On Mon, Jan 10, 2022 at 09:47:58PM +0800, Yu Kuai wrote:
> Throttled bios can't be issued after del_gendisk() is done, thus
> it's better to cancel them immediately rather than waiting for
> throttle is done.
>
> For example, if user thread is throttled with low bps while it's
> issuing large io, and the device is deleted. The user thread will
> wait for a long time for io to return.
>
> Noted this patch is mainly from revertion of commit 32e3374304c7
> ("blk-throttle: remove tg_drain_bios") and commit b77412372b68
> ("blk-throttle: remove blk_throtl_drain").
>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
> block/blk-throttle.c | 77 ++++++++++++++++++++++++++++++++++++++++++++
> block/blk-throttle.h | 2 ++
> block/genhd.c | 2 ++
> 3 files changed, 81 insertions(+)

Just wondering why not take the built-in way in throtl_upgrade_state() for
canceling throttled bios? Something like the following, then we can avoid
to re-invent the wheel.

block/blk-throttle.c | 38 +++++++++++++++++++++++++++++++-------
block/blk-throttle.h | 2 ++
block/genhd.c | 3 +++
3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index cf7e20804f1b..17e56b2e44c4 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1816,16 +1816,11 @@ static void throtl_upgrade_check(struct throtl_grp *tg)
throtl_upgrade_state(tg->td);
}

-static void throtl_upgrade_state(struct throtl_data *td)
+static void __throtl_cancel_bios(struct throtl_data *td)
{
struct cgroup_subsys_state *pos_css;
struct blkcg_gq *blkg;

- throtl_log(&td->service_queue, "upgrade to max");
- td->limit_index = LIMIT_MAX;
- td->low_upgrade_time = jiffies;
- td->scale = 0;
- rcu_read_lock();
blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) {
struct throtl_grp *tg = blkg_to_tg(blkg);
struct throtl_service_queue *sq = &tg->service_queue;
@@ -1834,12 +1829,41 @@ static void throtl_upgrade_state(struct throtl_data *td)
throtl_select_dispatch(sq);
throtl_schedule_next_dispatch(sq, true);
}
- rcu_read_unlock();
throtl_select_dispatch(&td->service_queue);
throtl_schedule_next_dispatch(&td->service_queue, true);
queue_work(kthrotld_workqueue, &td->dispatch_work);
}

+void blk_throtl_cancel_bios(struct request_queue *q)
+{
+ struct cgroup_subsys_state *pos_css;
+ struct blkcg_gq *blkg;
+
+ rcu_read_lock();
+ spin_lock_irq(&q->queue_lock);
+ __throtl_cancel_bios(q->td);
+ spin_unlock_irq(&q->queue_lock);
+ rcu_read_unlock();
+
+ blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg)
+ del_timer_sync(&blkg_to_tg(blkg)->service_queue.pending_timer);
+ del_timer_sync(&q->td->service_queue.pending_timer);
+
+ throtl_shutdown_wq(q);
+}
+
+static void throtl_upgrade_state(struct throtl_data *td)
+{
+ throtl_log(&td->service_queue, "upgrade to max");
+ td->limit_index = LIMIT_MAX;
+ td->low_upgrade_time = jiffies;
+ td->scale = 0;
+
+ rcu_read_lock();
+ __throtl_cancel_bios(td);
+ rcu_read_unlock();
+}
+
static void throtl_downgrade_state(struct throtl_data *td)
{
td->scale /= 2;
diff --git a/block/blk-throttle.h b/block/blk-throttle.h
index b23a9f3abb82..525ac607c518 100644
--- a/block/blk-throttle.h
+++ b/block/blk-throttle.h
@@ -162,11 +162,13 @@ static inline int blk_throtl_init(struct request_queue *q) { return 0; }
static inline void blk_throtl_exit(struct request_queue *q) { }
static inline void blk_throtl_register_queue(struct request_queue *q) { }
static inline bool blk_throtl_bio(struct bio *bio) { return false; }
+static inline void blk_throtl_cancel_bios(struct request_queue *q) {}
#else /* CONFIG_BLK_DEV_THROTTLING */
int blk_throtl_init(struct request_queue *q);
void blk_throtl_exit(struct request_queue *q);
void blk_throtl_register_queue(struct request_queue *q);
bool __blk_throtl_bio(struct bio *bio);
+void blk_throtl_cancel_bios(struct request_queue *q);
static inline bool blk_throtl_bio(struct bio *bio)
{
struct throtl_grp *tg = blkg_to_tg(bio->bi_blkg);
diff --git a/block/genhd.c b/block/genhd.c
index 626c8406f21a..1395cbd8eacf 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -30,6 +30,7 @@
#include "blk.h"
#include "blk-mq-sched.h"
#include "blk-rq-qos.h"
+#include "blk-throttle.h"

static struct kobject *block_depr;

@@ -622,6 +623,8 @@ void del_gendisk(struct gendisk *disk)

blk_mq_freeze_queue_wait(q);

+ blk_throtl_cancel_bios(q);
+
rq_qos_exit(q);
blk_sync_queue(q);
blk_flush_integrity();

Thanks,
Ming