Instead of allowing requests that are not power management requests
to enter the queue in runtime suspended status (RPM_SUSPENDED), make
the blk_get_request() caller block. This change fixes a starvation
issue: it is now guaranteed that power management requests will be
executed no matter how many blk_get_request() callers are waiting.
For blk-mq, instead of maintaining the q->nr_pending counter, rely
on q->q_usage_counter. Call pm_runtime_mark_last_busy() every time a
request finishes instead of only if the queue depth drops to zero.
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
---
block/blk-core.c | 37 ++++++++-----------------------------
block/blk-pm.c | 44 +++++++++++++++++++++++++++++++++++++++-----
2 files changed, 47 insertions(+), 34 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index fec135ae52cf..16dd3a989753 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2746,30 +2746,6 @@ void blk_account_io_done(struct request *req, u64 now)
}
}
-#ifdef CONFIG_PM
-/*
- * Don't process normal requests when queue is suspended
- * or in the process of suspending/resuming
- */
-static bool blk_pm_allow_request(struct request *rq)
-{
- switch (rq->q->rpm_status) {
- case RPM_RESUMING:
- case RPM_SUSPENDING:
- return rq->rq_flags & RQF_PM;
- case RPM_SUSPENDED:
- return false;
- default:
- return true;
- }
-}
-#else
-static bool blk_pm_allow_request(struct request *rq)
-{
- return true;
-}
-#endif
-
void blk_account_io_start(struct request *rq, bool new_io)
{
struct hd_struct *part;
@@ -2815,11 +2791,14 @@ static struct request *elv_next_request(struct request_queue *q)
while (1) {
list_for_each_entry(rq, &q->queue_head, queuelist) {
- if (blk_pm_allow_request(rq))
- return rq;
-
- if (rq->rq_flags & RQF_SOFTBARRIER)
- break;
+#ifdef CONFIG_PM
+ /*
+ * If a request gets queued in state RPM_SUSPENDED
+ * then that's a kernel bug.
+ */
+ WARN_ON_ONCE(q->rpm_status == RPM_SUSPENDED);
+#endif
+ return rq;
}
/*
diff --git a/block/blk-pm.c b/block/blk-pm.c
index 9b636960d285..972fbc656846 100644
--- a/block/blk-pm.c
+++ b/block/blk-pm.c
@@ -1,8 +1,11 @@
// SPDX-License-Identifier: GPL-2.0
+#include <linux/blk-mq.h>
#include <linux/blk-pm.h>
#include <linux/blkdev.h>
#include <linux/pm_runtime.h>
+#include "blk-mq.h"
+#include "blk-mq-tag.h"
/**
* blk_pm_runtime_init - Block layer runtime PM initialization routine
@@ -68,14 +71,40 @@ int blk_pre_runtime_suspend(struct request_queue *q)
if (!q->dev)
return ret;
+ WARN_ON_ONCE(q->rpm_status != RPM_ACTIVE);
+
+ /*
+ * Increase the pm_only counter before checking whether any
+ * non-PM blk_queue_enter() calls are in progress to avoid that any
+ * new non-PM blk_queue_enter() calls succeed before the pm_only
+ * counter is decreased again.
+ */
+ blk_set_pm_only(q);
+ ret = -EBUSY;
+ /* Switch q_usage_counter from per-cpu to atomic mode. */
+ blk_freeze_queue_start(q);
+ /*
+ * Wait until atomic mode has been reached. Since that
+ * involves calling call_rcu(), it is guaranteed that later
+ * blk_queue_enter() calls see the pm-only state. See also
+ * http://lwn.net/Articles/573497/.
+ */
+ percpu_ref_switch_to_atomic_sync(&q->q_usage_counter);
+ if (percpu_ref_is_zero(&q->q_usage_counter))
+ ret = 0;
+ /* Switch q_usage_counter back to per-cpu mode. */
+ blk_mq_unfreeze_queue(q);
+
spin_lock_irq(q->queue_lock);
- if (q->nr_pending) {
- ret = -EBUSY;
+ if (ret < 0)
pm_runtime_mark_last_busy(q->dev);
- } else {
+ else
q->rpm_status = RPM_SUSPENDING;
- }
spin_unlock_irq(q->queue_lock);
+
+ if (ret)
+ blk_clear_pm_only(q);
+
return ret;
}
EXPORT_SYMBOL(blk_pre_runtime_suspend);
@@ -106,6 +135,9 @@ void blk_post_runtime_suspend(struct request_queue *q, int err)
pm_runtime_mark_last_busy(q->dev);
}
spin_unlock_irq(q->queue_lock);
+
+ if (err)
+ blk_clear_pm_only(q);
}
EXPORT_SYMBOL(blk_post_runtime_suspend);
@@ -153,13 +185,15 @@ void blk_post_runtime_resume(struct request_queue *q, int err)
spin_lock_irq(q->queue_lock);
if (!err) {
q->rpm_status = RPM_ACTIVE;
- __blk_run_queue(q);
pm_runtime_mark_last_busy(q->dev);
pm_request_autosuspend(q->dev);
} else {
q->rpm_status = RPM_SUSPENDED;
}
spin_unlock_irq(q->queue_lock);
+
+ if (!err)
+ blk_clear_pm_only(q);
}
EXPORT_SYMBOL(blk_post_runtime_resume);
--
2.19.0.444.g18242da7ef-goog
