block: Make blk_get_request() block for non-PM requests while suspended

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@acm.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index fec135a..16dd3a9 100644 (file)
--- 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 9b63696..972fbc6 100644 (file)
--- 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);