ide: dequeue in-flight request

ide generally has single request in flight and tracks it using
hwif->rq and all state handlers follow the following convention.

* ide_started is returned if the request is in flight.

* ide_stopped is returned if the queue needs to be restarted.  The
  request might or might not have been processed fully or partially.

* hwif->rq is set to NULL, when an issued request completes.

So, dequeueing model can be implemented by dequeueing after fetch,
requeueing if hwif->rq isn't NULL on ide_stopped return and doing
about the same thing on completion / port unlock paths.  These changes
can be made in ide-io proper.

In addition to the above main changes, the following updates are
necessary.

* ide-cd shouldn't dequeue a request when issuing REQUEST SENSE for it
  as the request is already dequeued.

* ide-atapi uses request queue as stack when issuing REQUEST SENSE to
  put the REQUEST SENSE in front of the failed request.  This now
  needs to be done using requeueing.

[ Impact: dequeue in-flight request ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Borislav Petkov <petkovbb@googlemail.com>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 39 insertions, 17 deletions

diff --git a/drivers/ide/ide-atapi.c b/drivers/ide/ide-atapi.c
index 792534db8f85..2874c3d703a9 100644
--- a/drivers/ide/ide-atapi.c
+++ b/drivers/ide/ide-atapi.c
@@ -246,6 +246,7 @@ EXPORT_SYMBOL_GPL(ide_queue_sense_rq);
  */
 void ide_retry_pc(ide_drive_t *drive)
 {
+        struct request *failed_rq = drive->hwif->rq;
         struct request *sense_rq = &drive->sense_rq;
         struct ide_atapi_pc *pc = &drive->request_sense_pc;
 
@@ -260,8 +261,17 @@ void ide_retry_pc(ide_drive_t *drive)
         if (drive->media == ide_tape)
                 set_bit(IDE_AFLAG_IGNORE_DSC, &drive->atapi_flags);
 
-        if (ide_queue_sense_rq(drive, pc))
-                ide_complete_rq(drive, -EIO, blk_rq_bytes(drive->hwif->rq));
+        /*
+         * Push back the failed request and put request sense on top
+         * of it.  The failed command will be retried after sense data
+         * is acquired.
+         */
+        blk_requeue_request(failed_rq->q, failed_rq);
+        drive->hwif->rq = NULL;
+        if (ide_queue_sense_rq(drive, pc)) {
+                blkdev_dequeue_request(failed_rq);
+                ide_complete_rq(drive, -EIO, blk_rq_bytes(failed_rq));
+        }
 }
 EXPORT_SYMBOL_GPL(ide_retry_pc);
 
diff --git a/drivers/ide/ide-cd.c b/drivers/ide/ide-cd.c
index 2eadc9d2e965..4c7792fd5f93 100644
--- a/drivers/ide/ide-cd.c
+++ b/drivers/ide/ide-cd.c
@@ -405,15 +405,7 @@ static int cdrom_decode_status(ide_drive_t *drive, u8 stat)
 
 end_request:
         if (stat & ATA_ERR) {
-                struct request_queue *q = drive->queue;
-                unsigned long flags;
-
-                spin_lock_irqsave(q->queue_lock, flags);
-                blkdev_dequeue_request(rq);
-                spin_unlock_irqrestore(q->queue_lock, flags);
-
                 hwif->rq = NULL;
-
                 return ide_queue_sense_rq(drive, rq) ? 2 : 1;
         } else
                 return 2;
diff --git a/drivers/ide/ide-io.c b/drivers/ide/ide-io.c
index ca2519d7b994..abda7337b3f4 100644
--- a/drivers/ide/ide-io.c
+++ b/drivers/ide/ide-io.c
@@ -487,10 +487,10 @@ void do_ide_request(struct request_queue *q)
 
         if (!ide_lock_port(hwif)) {
                 ide_hwif_t *prev_port;
+
+                WARN_ON_ONCE(hwif->rq);
 repeat:
                 prev_port = hwif->host->cur_port;
-                hwif->rq = NULL;
-
                 if (drive->dev_flags & IDE_DFLAG_SLEEPING &&
                     time_after(drive->sleep, jiffies)) {
                         ide_unlock_port(hwif);
@@ -519,7 +519,12 @@ repeat:
                  * we know that the queue isn't empty, but this can happen
                  * if the q->prep_rq_fn() decides to kill a request
                  */
-                rq = elv_next_request(drive->queue);
+                if (!rq) {
+                        rq = elv_next_request(drive->queue);
+                        if (rq)
+                                blkdev_dequeue_request(rq);
+                }
+
                 spin_unlock_irq(q->queue_lock);
                 spin_lock_irq(&hwif->lock);
 
@@ -555,8 +560,11 @@ repeat:
                 startstop = start_request(drive, rq);
                 spin_lock_irq(&hwif->lock);
 
-                if (startstop == ide_stopped)
+                if (startstop == ide_stopped) {
+                        rq = hwif->rq;
+                        hwif->rq = NULL;
                         goto repeat;
+                }
         } else
                 goto plug_device;
 out:
@@ -572,18 +580,24 @@ plug_device:
 plug_device_2:
         spin_lock_irq(q->queue_lock);
 
+        if (rq)
+                blk_requeue_request(q, rq);
         if (!elv_queue_empty(q))
                 blk_plug_device(q);
 }
 
-static void ide_plug_device(ide_drive_t *drive)
+static void ide_requeue_and_plug(ide_drive_t *drive, struct request *rq)
 {
         struct request_queue *q = drive->queue;
         unsigned long flags;
 
         spin_lock_irqsave(q->queue_lock, flags);
+
+        if (rq)
+                blk_requeue_request(q, rq);
         if (!elv_queue_empty(q))
                 blk_plug_device(q);
+
         spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
@@ -632,6 +646,7 @@ void ide_timer_expiry (unsigned long data)
         unsigned long   flags;
         int             wait = -1;
         int             plug_device = 0;
+        struct request  *uninitialized_var(rq_in_flight);
 
         spin_lock_irqsave(&hwif->lock, flags);
 
@@ -693,6 +708,8 @@ void ide_timer_expiry (unsigned long data)
                 spin_lock_irq(&hwif->lock);
                 enable_irq(hwif->irq);
                 if (startstop == ide_stopped) {
+                        rq_in_flight = hwif->rq;
+                        hwif->rq = NULL;
                         ide_unlock_port(hwif);
                         plug_device = 1;
                 }
@@ -701,7 +718,7 @@ void ide_timer_expiry (unsigned long data)
 
         if (plug_device) {
                 ide_unlock_host(hwif->host);
-                ide_plug_device(drive);
+                ide_requeue_and_plug(drive, rq_in_flight);
         }
 }
 
@@ -787,6 +804,7 @@ irqreturn_t ide_intr (int irq, void *dev_id)
         ide_startstop_t startstop;
         irqreturn_t irq_ret = IRQ_NONE;
         int plug_device = 0;
+        struct request *uninitialized_var(rq_in_flight);
 
         if (host->host_flags & IDE_HFLAG_SERIALIZE) {
                 if (hwif != host->cur_port)
@@ -866,6 +884,8 @@ irqreturn_t ide_intr (int irq, void *dev_id)
          */
         if (startstop == ide_stopped) {
                 BUG_ON(hwif->handler);
+                rq_in_flight = hwif->rq;
+                hwif->rq = NULL;
                 ide_unlock_port(hwif);
                 plug_device = 1;
         }
@@ -875,7 +895,7 @@ out:
 out_early:
         if (plug_device) {
                 ide_unlock_host(hwif->host);
-                ide_plug_device(drive);
+                ide_requeue_and_plug(drive, rq_in_flight);
         }
 
         return irq_ret;