md: handle_stripe5 - add request/completion logic for async read ops

When a read bio is attached to the stripe and the corresponding block is
marked R5_UPTODATE, then a read (biofill) operation is scheduled to copy
the data from the stripe cache to the bio buffer.  handle_stripe flags the
blocks to be operated on with the R5_Wantfill flag.  If new read requests
arrive while raid5_run_ops is running they will not be handled until
handle_stripe is scheduled to run again.

Changelog:
* cleanup to_read and to_fill accounting
* do not fail reads that have reached the cache

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-By: NeilBrown <neilb@suse.de>

1 files changed, 25 insertions, 28 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 810cf831edda..a33dac7c2e2f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2049,9 +2049,12 @@ handle_requests_to_failed_array(raid5_conf_t *conf, struct stripe_head *sh,
                         bi = bi2;
                 }
 
-                /* fail any reads if this device is non-operational */
-                if (!test_bit(R5_Insync, &sh->dev[i].flags) ||
-                    test_bit(R5_ReadError, &sh->dev[i].flags)) {
+                /* fail any reads if this device is non-operational and
+                 * the data has not reached the cache yet.
+                 */
+                if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
+                    (!test_bit(R5_Insync, &sh->dev[i].flags) ||
+                      test_bit(R5_ReadError, &sh->dev[i].flags))) {
                         bi = sh->dev[i].toread;
                         sh->dev[i].toread = NULL;
                         if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
@@ -2740,37 +2743,27 @@ static void handle_stripe5(struct stripe_head *sh)
                 struct r5dev *dev = &sh->dev[i];
                 clear_bit(R5_Insync, &dev->flags);
 
-                pr_debug("check %d: state 0x%lx read %p write %p written %p\n",
-                        i, dev->flags, dev->toread, dev->towrite, dev->written);
-                /* maybe we can reply to a read */
-                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
-                        struct bio *rbi, *rbi2;
-                        pr_debug("Return read for disc %d\n", i);
-                        spin_lock_irq(&conf->device_lock);
-                        rbi = dev->toread;
-                        dev->toread = NULL;
-                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
-                                wake_up(&conf->wait_for_overlap);
-                        spin_unlock_irq(&conf->device_lock);
-                        while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
-                                copy_data(0, rbi, dev->page, dev->sector);
-                                rbi2 = r5_next_bio(rbi, dev->sector);
-                                spin_lock_irq(&conf->device_lock);
-                                if (--rbi->bi_phys_segments == 0) {
-                                        rbi->bi_next = return_bi;
-                                        return_bi = rbi;
-                                }
-                                spin_unlock_irq(&conf->device_lock);
-                                rbi = rbi2;
-                        }
-                }
+                pr_debug("check %d: state 0x%lx toread %p read %p write %p "
+                        "written %p\n", i, dev->flags, dev->toread, dev->read,
+                        dev->towrite, dev->written);
+
+                /* maybe we can request a biofill operation
+                 *
+                 * new wantfill requests are only permitted while
+                 * STRIPE_OP_BIOFILL is clear
+                 */
+                if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread &&
+                        !test_bit(STRIPE_OP_BIOFILL, &sh->ops.pending))
+                        set_bit(R5_Wantfill, &dev->flags);
 
                 /* now count some things */
                 if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
                 if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;
                 if (test_bit(R5_Wantcompute, &dev->flags)) s.compute++;
 
-                if (dev->toread)
+                if (test_bit(R5_Wantfill, &dev->flags))
+                        s.to_fill++;
+                else if (dev->toread)
                         s.to_read++;
                 if (dev->towrite) {
                         s.to_write++;
@@ -2793,6 +2786,10 @@ static void handle_stripe5(struct stripe_head *sh)
                         set_bit(R5_Insync, &dev->flags);
         }
         rcu_read_unlock();
+
+        if (s.to_fill && !test_and_set_bit(STRIPE_OP_BIOFILL, &sh->ops.pending))
+                sh->ops.count++;
+
         pr_debug("locked=%d uptodate=%d to_read=%d"
                 " to_write=%d failed=%d failed_num=%d\n",
                 s.locked, s.uptodate, s.to_read, s.to_write,