[PATCH 7/9] blk-mq: Introduce blk_quiesce_queue() and blk_resume_queue()
Bart Van Assche
bart.vanassche at sandisk.com
Mon Sep 26 11:28:24 PDT 2016
blk_quiesce_queue() prevents that new queue_rq() invocations
occur and waits until ongoing invocations have finished. This
function does *not* wait until all outstanding requests have
finished (this means invocation of request.end_io()).
blk_resume_queue() resumes normal I/O processing.
Signed-off-by: Bart Van Assche <bart.vanassche at sandisk.com>
---
block/blk-core.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++----
block/blk-mq.c | 24 +++++++++++++-----
block/blk.h | 2 +-
include/linux/blkdev.h | 5 ++++
4 files changed, 85 insertions(+), 12 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 0ff5d57..62cb6ae 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -682,18 +682,20 @@ static void blk_queue_usage_counter_release(struct percpu_ref *ref)
wake_up_all(&q->freeze_wq);
}
-void blk_freeze_queue_start(struct request_queue *q)
+bool blk_freeze_queue_start(struct request_queue *q, bool kill_percpu_ref)
{
int freeze_depth;
freeze_depth = atomic_inc_return(&q->freeze_depth);
if (freeze_depth == 1) {
- percpu_ref_kill(&q->q_usage_counter);
+ if (kill_percpu_ref)
+ percpu_ref_kill(&q->q_usage_counter);
if (q->mq_ops)
blk_mq_run_hw_queues(q, false);
else if (q->request_fn)
blk_run_queue(q);
}
+ return freeze_depth == 1;
}
void blk_freeze_queue_wait(struct request_queue *q)
@@ -708,21 +710,75 @@ void blk_freeze_queue_wait(struct request_queue *q)
*/
void blk_freeze_queue(struct request_queue *q)
{
- blk_freeze_queue_start(q);
+ blk_freeze_queue_start(q, true);
blk_freeze_queue_wait(q);
}
-void blk_unfreeze_queue(struct request_queue *q)
+static bool __blk_unfreeze_queue(struct request_queue *q,
+ bool reinit_percpu_ref)
{
int freeze_depth;
freeze_depth = atomic_dec_return(&q->freeze_depth);
WARN_ON_ONCE(freeze_depth < 0);
if (!freeze_depth) {
- percpu_ref_reinit(&q->q_usage_counter);
+ if (reinit_percpu_ref)
+ percpu_ref_reinit(&q->q_usage_counter);
wake_up_all(&q->freeze_wq);
}
+ return freeze_depth == 0;
+}
+
+void blk_unfreeze_queue(struct request_queue *q)
+{
+ __blk_unfreeze_queue(q, true);
+}
+
+/**
+ * blk_quiesce_queue() - wait until all pending queue_rq calls have finished
+ *
+ * Prevent that new I/O requests are queued and wait until all pending
+ * queue_rq() calls have finished. Must not be called if the queue has already
+ * been frozen. Additionally, freezing the queue after having quiesced the
+ * queue and before resuming the queue is not allowed.
+ *
+ * Note: this function does not prevent that the struct request end_io()
+ * callback function is invoked.
+ */
+void blk_quiesce_queue(struct request_queue *q)
+{
+ spin_lock_irq(q->queue_lock);
+ WARN_ON_ONCE(blk_queue_quiescing(q));
+ queue_flag_set(QUEUE_FLAG_QUIESCING, q);
+ spin_unlock_irq(q->queue_lock);
+
+ WARN_ON_ONCE(!blk_freeze_queue_start(q, false));
+ synchronize_rcu();
+
+ spin_lock_irq(q->queue_lock);
+ WARN_ON_ONCE(!blk_queue_quiescing(q));
+ queue_flag_clear(QUEUE_FLAG_QUIESCING, q);
+ spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL_GPL(blk_quiesce_queue);
+
+/**
+ * blk_resume_queue() - resume request processing
+ *
+ * The caller is responsible for serializing blk_quiesce_queue() and
+ * blk_resume_queue().
+ */
+void blk_resume_queue(struct request_queue *q)
+{
+ WARN_ON_ONCE(!__blk_unfreeze_queue(q, false));
+ WARN_ON_ONCE(blk_queue_quiescing(q));
+
+ if (q->mq_ops)
+ blk_mq_run_hw_queues(q, false);
+ else
+ blk_run_queue(q);
}
+EXPORT_SYMBOL_GPL(blk_resume_queue);
static void blk_rq_timed_out_timer(unsigned long data)
{
diff --git a/block/blk-mq.c b/block/blk-mq.c
index e17a5bf..4df9e4f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -60,7 +60,7 @@ static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx,
void blk_mq_freeze_queue_start(struct request_queue *q)
{
- blk_freeze_queue_start(q);
+ blk_freeze_queue_start(q, true);
}
EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_start);
@@ -441,6 +441,9 @@ static void blk_mq_requeue_work(struct work_struct *work)
struct request *rq, *next;
unsigned long flags;
+ if (blk_queue_quiescing(q))
+ return;
+
spin_lock_irqsave(&q->requeue_lock, flags);
list_splice_init(&q->requeue_list, &rq_list);
spin_unlock_irqrestore(&q->requeue_lock, flags);
@@ -757,6 +760,8 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
*/
flush_busy_ctxs(hctx, &rq_list);
+ rcu_read_lock();
+
/*
* If we have previous entries on our dispatch list, grab them
* and stuff them at the front for more fair dispatch.
@@ -836,8 +841,11 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
*
* blk_mq_run_hw_queue() already checks the STOPPED bit
**/
- blk_mq_run_hw_queue(hctx, true);
+ if (!blk_queue_quiescing(q))
+ blk_mq_run_hw_queue(hctx, true);
}
+
+ rcu_read_unlock();
}
/*
@@ -1294,7 +1302,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
blk_mq_bio_to_request(rq, bio);
/*
- * We do limited pluging. If the bio can be merged, do that.
+ * We do limited plugging. If the bio can be merged, do that.
* Otherwise the existing request in the plug list will be
* issued. So the plug list will have one request at most
*/
@@ -1314,9 +1322,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
blk_mq_put_ctx(data.ctx);
if (!old_rq)
goto done;
- if (!blk_mq_direct_issue_request(old_rq, &cookie))
- goto done;
- blk_mq_insert_request(old_rq, false, true, true);
+
+ rcu_read_lock();
+ if (blk_queue_quiescing(q) ||
+ blk_mq_direct_issue_request(old_rq, &cookie) != 0)
+ blk_mq_insert_request(old_rq, false, true, true);
+ rcu_read_unlock();
+
goto done;
}
diff --git a/block/blk.h b/block/blk.h
index 12f7366..0e934b5 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -71,7 +71,7 @@ void __blk_queue_free_tags(struct request_queue *q);
bool __blk_end_bidi_request(struct request *rq, int error,
unsigned int nr_bytes, unsigned int bidi_bytes);
void blk_freeze_queue(struct request_queue *q);
-void blk_freeze_queue_start(struct request_queue *q);
+bool blk_freeze_queue_start(struct request_queue *q, bool kill_percpu_ref);
void blk_freeze_queue_wait(struct request_queue *q);
void blk_unfreeze_queue(struct request_queue *q);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f08dc65..06c9b21 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -505,6 +505,7 @@ struct request_queue {
#define QUEUE_FLAG_FUA 24 /* device supports FUA writes */
#define QUEUE_FLAG_FLUSH_NQ 25 /* flush not queueuable */
#define QUEUE_FLAG_DAX 26 /* device supports DAX */
+#define QUEUE_FLAG_QUIESCING 27
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \
@@ -595,6 +596,8 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
#define blk_queue_secure_erase(q) \
(test_bit(QUEUE_FLAG_SECERASE, &(q)->queue_flags))
#define blk_queue_dax(q) test_bit(QUEUE_FLAG_DAX, &(q)->queue_flags)
+#define blk_queue_quiescing(q) test_bit(QUEUE_FLAG_QUIESCING, \
+ &(q)->queue_flags)
#define blk_noretry_request(rq) \
((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
@@ -824,6 +827,8 @@ extern void __blk_run_queue(struct request_queue *q);
extern void __blk_run_queue_uncond(struct request_queue *q);
extern void blk_run_queue(struct request_queue *);
extern void blk_run_queue_async(struct request_queue *q);
+extern void blk_quiesce_queue(struct request_queue *q);
+extern void blk_resume_queue(struct request_queue *q);
extern int blk_rq_map_user(struct request_queue *, struct request *,
struct rq_map_data *, void __user *, unsigned long,
gfp_t);
--
2.10.0
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