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Subject[PATCH 06/10] block: reorganize queue draining
Date
Reorganize queue draining related code in preparation of queue exit
changes.

* Factor out actual draining from elv_quiesce_start() to
blk_drain_queue().

* Make elv_quiesce_start/end() responsible for their own locking.

* Replace open-coded ELVSWITCH clearing in elevator_switch() with
elv_quiesce_end().

This patch doesn't cause any visible functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
---
block/blk-core.c | 28 ++++++++++++++++++++++++++++
block/blk.h | 1 +
block/elevator.c | 37 +++++++++++--------------------------
3 files changed, 40 insertions(+), 26 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index fafa669..50e3144 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -28,6 +28,7 @@
#include <linux/task_io_accounting_ops.h>
#include <linux/fault-inject.h>
#include <linux/list_sort.h>
+#include <linux/delay.h>

#define CREATE_TRACE_POINTS
#include <trace/events/block.h>
@@ -345,6 +346,33 @@ void blk_put_queue(struct request_queue *q)
}
EXPORT_SYMBOL(blk_put_queue);

+/**
+ * blk_drain_queue - drain requests from request_queue
+ * @q: queue to drain
+ *
+ * Drain ELV_PRIV requests from @q. The caller is responsible for ensuring
+ * that no new requests which need to be drained are queued.
+ */
+void blk_drain_queue(struct request_queue *q)
+{
+ while (true) {
+ int nr_rqs;
+
+ spin_lock_irq(q->queue_lock);
+
+ elv_drain_elevator(q);
+
+ __blk_run_queue(q);
+ nr_rqs = q->rq.elvpriv;
+
+ spin_unlock_irq(q->queue_lock);
+
+ if (!nr_rqs)
+ break;
+ msleep(10);
+ }
+}
+
/*
* Note: If a driver supplied the queue lock, it should not zap that lock
* unexpectedly as some queue cleanup components like elevator_exit() and
diff --git a/block/blk.h b/block/blk.h
index da247ba..2b66dc2 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -15,6 +15,7 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
struct bio *bio);
int blk_rq_append_bio(struct request_queue *q, struct request *rq,
struct bio *bio);
+void blk_drain_queue(struct request_queue *q);
void blk_dequeue_request(struct request *rq);
void __blk_queue_free_tags(struct request_queue *q);
bool __blk_end_bidi_request(struct request *rq, int error,
diff --git a/block/elevator.c b/block/elevator.c
index cb332cb..74a277f 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -31,7 +31,6 @@
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
-#include <linux/delay.h>
#include <linux/blktrace_api.h>
#include <linux/hash.h>
#include <linux/uaccess.h>
@@ -606,43 +605,35 @@ void elv_requeue_request(struct request_queue *q, struct request *rq)
void elv_drain_elevator(struct request_queue *q)
{
static int printed;
+
+ lockdep_assert_held(q->queue_lock);
+
while (q->elevator->ops->elevator_dispatch_fn(q, 1))
;
- if (q->nr_sorted == 0)
- return;
- if (printed++ < 10) {
+ if (q->nr_sorted && printed++ < 10) {
printk(KERN_ERR "%s: forced dispatching is broken "
"(nr_sorted=%u), please report this\n",
q->elevator->elevator_type->elevator_name, q->nr_sorted);
}
}

-/*
- * Call with queue lock held, interrupts disabled
- */
void elv_quiesce_start(struct request_queue *q)
{
if (!q->elevator)
return;

+ spin_lock_irq(q->queue_lock);
queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
+ spin_unlock_irq(q->queue_lock);

- /*
- * make sure we don't have any requests in flight
- */
- elv_drain_elevator(q);
- while (q->rq.elvpriv) {
- __blk_run_queue(q);
- spin_unlock_irq(q->queue_lock);
- msleep(10);
- spin_lock_irq(q->queue_lock);
- elv_drain_elevator(q);
- }
+ blk_drain_queue(q);
}

void elv_quiesce_end(struct request_queue *q)
{
+ spin_lock_irq(q->queue_lock);
queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+ spin_unlock_irq(q->queue_lock);
}

void __elv_add_request(struct request_queue *q, struct request *rq, int where)
@@ -972,7 +963,6 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
/*
* Turn on BYPASS and drain all requests w/ elevator private data
*/
- spin_lock_irq(q->queue_lock);
elv_quiesce_start(q);

/*
@@ -983,8 +973,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
/*
* attach and start new elevator
*/
+ spin_lock_irq(q->queue_lock);
elevator_attach(q, e, data);
-
spin_unlock_irq(q->queue_lock);

if (old_elevator->registered) {
@@ -999,9 +989,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
* finally exit old elevator and turn off BYPASS.
*/
elevator_exit(old_elevator);
- spin_lock_irq(q->queue_lock);
elv_quiesce_end(q);
- spin_unlock_irq(q->queue_lock);

blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);

@@ -1015,10 +1003,7 @@ fail_register:
elevator_exit(e);
q->elevator = old_elevator;
elv_register_queue(q);
-
- spin_lock_irq(q->queue_lock);
- queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
- spin_unlock_irq(q->queue_lock);
+ elv_quiesce_end(q);

return err;
}
--
1.7.3.1


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