[PATCH v2] block: fix peeking requests during PM

[Christoph Hellwig]

We need to look for an active PM request until the next softbarrier
instead of looking for the first non-PM request.  Otherwise any cause
of request reordering might starve the PM request(s).

Signed-off-by: Christoph Hellwig <h...@lst.de>
---
 block/blk-core.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 14f7674fa0b1..480029e4fb54 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2464,20 +2464,22 @@ void blk_account_io_done(struct request *req)
  * Don't process normal requests when queue is suspended
  * or in the process of suspending/resuming
  */
-static struct request *blk_pm_peek_request(struct request_queue *q,
-                                          struct request *rq)
+static bool blk_pm_allow_request(struct request *rq)
 {
-       if (q->dev && (q->rpm_status == RPM_SUSPENDED ||
-           (q->rpm_status != RPM_ACTIVE && !(rq->rq_flags & RQF_PM))))
-               return NULL;
-       else
-               return rq;
+       switch (rq->q->rpm_status) {
+       case RPM_RESUMING:
+       case RPM_SUSPENDING:
+               return rq->rq_flags & RQF_PM;
+       case RPM_SUSPENDED:
+               return false;
+       }
+
+       return true;
 }
 #else
-static inline struct request *blk_pm_peek_request(struct request_queue *q,
-                                                 struct request *rq)
+static bool blk_pm_allow_request(struct request *rq)
 {
-       return rq;
+       return true;
 }
 #endif
 
@@ -2525,9 +2527,12 @@ static struct request *elv_next_request(struct 
request_queue *q)
        WARN_ON_ONCE(q->mq_ops);
 
        while (1) {
-               if (!list_empty(&q->queue_head)) {
-                       rq = list_entry_rq(q->queue_head.next);
-                       return rq;
+               list_for_each_entry(rq, &q->queue_head, queuelist) {
+                       if (blk_pm_allow_request(rq))
+                               return rq;
+
+                       if (rq->rq_flags & RQF_SOFTBARRIER)
+                               break;
                }
 
                /*
@@ -2578,10 +2583,6 @@ struct request *blk_peek_request(struct request_queue *q)
        WARN_ON_ONCE(q->mq_ops);
 
        while ((rq = elv_next_request(q)) != NULL) {
-               rq = blk_pm_peek_request(q, rq);
-               if (!rq)
-                       break;
-
                if (!(rq->rq_flags & RQF_STARTED)) {
                        /*
                         * This is the first time the device driver
-- 
2.14.2