[PATCH] md: allow reads that have bypassed the cache to be retried on failure

If a bypass-the-cache read fails, we simply try again through the cache.  If
it fails again it will trigger normal recovery precedures.

update 1:

From: NeilBrown <neilb@suse.de>

1/
  chunk_aligned_read and retry_aligned_read assume that
      data_disks == raid_disks - 1
  which is not true for raid6.
  So when an aligned read request bypasses the cache, we can get the wrong data.

2/ The cloned bio is being used-after-free in raid5_align_endio
   (to test BIO_UPTODATE).

3/ We forgot to add rdev->data_offset when submitting
   a bio for aligned-read

4/ clone_bio calls blk_recount_segments and then we change bi_bdev,
   so we need to invalidate the segment counts.

5/ We don't de-reference the rdev when the read completes.
   This means we need to record the rdev to so it is still
   available in the end_io routine.  Fortunately
   bi_next in the original bio is unused at this point so
   we can stuff it in there.

6/ We leak a cloned bio if the target rdev is not usable.

From: NeilBrown <neilb@suse.de>

update 2:

1/ When aligned requests fail (read error) they need to be retried
   via the normal method (stripe cache).  As we cannot be sure that
   we can process a single read in one go (we may not be able to
   allocate all the stripes needed) we store a bio-being-retried
   and a list of bioes-that-still-need-to-be-retried.
   When find a bio that needs to be retried, we should add it to
   the list, not to single-bio...

2/ We were never incrementing 'scnt' when resubmitting failed
   aligned requests.

[akpm@osdl.org: build fix]
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 269b777..2ac2e56 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -134,6 +134,8 @@ static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
                        if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
                                list_add_tail(&sh->lru, &conf->inactive_list);
                                wake_up(&conf->wait_for_stripe);
+                               if (conf->retry_read_aligned)
+                                       md_wakeup_thread(conf->mddev->thread);
                        }
                }
        }
@@ -2644,19 +2646,81 @@ static int in_chunk_boundary(mddev_t *mddev, struct bio *bio)
                ((sector & (chunk_sectors - 1)) + bio_sectors);
 }
 
+/*
+ *  add bio to the retry LIFO  ( in O(1) ... we are in interrupt )
+ *  later sampled by raid5d.
+ */
+static void add_bio_to_retry(struct bio *bi,raid5_conf_t *conf)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&conf->device_lock, flags);
+
+       bi->bi_next = conf->retry_read_aligned_list;
+       conf->retry_read_aligned_list = bi;
+
+       spin_unlock_irqrestore(&conf->device_lock, flags);
+       md_wakeup_thread(conf->mddev->thread);
+}
+
+
+static struct bio *remove_bio_from_retry(raid5_conf_t *conf)
+{
+       struct bio *bi;
+
+       bi = conf->retry_read_aligned;
+       if (bi) {
+               conf->retry_read_aligned = NULL;
+               return bi;
+       }
+       bi = conf->retry_read_aligned_list;
+       if(bi) {
+               conf->retry_read_aligned = bi->bi_next;
+               bi->bi_next = NULL;
+               bi->bi_phys_segments = 1; /* biased count of active stripes */
+               bi->bi_hw_segments = 0; /* count of processed stripes */
+       }
+
+       return bi;
+}
+
+
 /*
  *  The "raid5_align_endio" should check if the read succeeded and if it
  *  did, call bio_endio on the original bio (having bio_put the new bio
  *  first).
  *  If the read failed..
  */
-int raid5_align_endio(struct bio *bi, unsigned int bytes , int error)
+static int raid5_align_endio(struct bio *bi, unsigned int bytes, int error)
 {
        struct bio* raid_bi  = bi->bi_private;
+       mddev_t *mddev;
+       raid5_conf_t *conf;
+       int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+       mdk_rdev_t *rdev;
+
        if (bi->bi_size)
                return 1;
        bio_put(bi);
-       bio_endio(raid_bi, bytes, error);
+
+       mddev = raid_bi->bi_bdev->bd_disk->queue->queuedata;
+       conf = mddev_to_conf(mddev);
+       rdev = (void*)raid_bi->bi_next;
+       raid_bi->bi_next = NULL;
+
+       rdev_dec_pending(rdev, conf->mddev);
+
+       if (!error && uptodate) {
+               bio_endio(raid_bi, bytes, 0);
+               if (atomic_dec_and_test(&conf->active_aligned_reads))
+                       wake_up(&conf->wait_for_stripe);
+               return 0;
+       }
+
+
+       PRINTK("raid5_align_endio : io error...handing IO for a retry\n");
+
+       add_bio_to_retry(raid_bi, conf);
        return 0;
 }
 
@@ -2665,7 +2729,7 @@ static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
        mddev_t *mddev = q->queuedata;
        raid5_conf_t *conf = mddev_to_conf(mddev);
        const unsigned int raid_disks = conf->raid_disks;
-       const unsigned int data_disks = raid_disks - 1;
+       const unsigned int data_disks = raid_disks - conf->max_degraded;
        unsigned int dd_idx, pd_idx;
        struct bio* align_bi;
        mdk_rdev_t *rdev;
@@ -2699,13 +2763,25 @@ static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
        rcu_read_lock();
        rdev = rcu_dereference(conf->disks[dd_idx].rdev);
        if (rdev && test_bit(In_sync, &rdev->flags)) {
-               align_bi->bi_bdev =  rdev->bdev;
                atomic_inc(&rdev->nr_pending);
                rcu_read_unlock();
+               raid_bio->bi_next = (void*)rdev;
+               align_bi->bi_bdev =  rdev->bdev;
+               align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
+               align_bi->bi_sector += rdev->data_offset;
+
+               spin_lock_irq(&conf->device_lock);
+               wait_event_lock_irq(conf->wait_for_stripe,
+                                   conf->quiesce == 0,
+                                   conf->device_lock, /* nothing */);
+               atomic_inc(&conf->active_aligned_reads);
+               spin_unlock_irq(&conf->device_lock);
+
                generic_make_request(align_bi);
                return 1;
        } else {
                rcu_read_unlock();
+               bio_put(align_bi);
                return 0;
        }
 }
@@ -3050,6 +3126,72 @@ static inline sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *ski
        return STRIPE_SECTORS;
 }
 
+static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
+{
+       /* We may not be able to submit a whole bio at once as there
+        * may not be enough stripe_heads available.
+        * We cannot pre-allocate enough stripe_heads as we may need
+        * more than exist in the cache (if we allow ever large chunks).
+        * So we do one stripe head at a time and record in
+        * ->bi_hw_segments how many have been done.
+        *
+        * We *know* that this entire raid_bio is in one chunk, so
+        * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
+        */
+       struct stripe_head *sh;
+       int dd_idx, pd_idx;
+       sector_t sector, logical_sector, last_sector;
+       int scnt = 0;
+       int remaining;
+       int handled = 0;
+
+       logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
+       sector = raid5_compute_sector(  logical_sector,
+                                       conf->raid_disks,
+                                       conf->raid_disks - conf->max_degraded,
+                                       &dd_idx,
+                                       &pd_idx,
+                                       conf);
+       last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);
+
+       for (; logical_sector < last_sector;
+            logical_sector += STRIPE_SECTORS, scnt++) {
+
+               if (scnt < raid_bio->bi_hw_segments)
+                       /* already done this stripe */
+                       continue;
+
+               sh = get_active_stripe(conf, sector, conf->raid_disks, pd_idx, 1);
+
+               if (!sh) {
+                       /* failed to get a stripe - must wait */
+                       raid_bio->bi_hw_segments = scnt;
+                       conf->retry_read_aligned = raid_bio;
+                       return handled;
+               }
+
+               set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
+               add_stripe_bio(sh, raid_bio, dd_idx, 0);
+               handle_stripe(sh, NULL);
+               release_stripe(sh);
+               handled++;
+       }
+       spin_lock_irq(&conf->device_lock);
+       remaining = --raid_bio->bi_phys_segments;
+       spin_unlock_irq(&conf->device_lock);
+       if (remaining == 0) {
+               int bytes = raid_bio->bi_size;
+
+               raid_bio->bi_size = 0;
+               raid_bio->bi_end_io(raid_bio, bytes, 0);
+       }
+       if (atomic_dec_and_test(&conf->active_aligned_reads))
+               wake_up(&conf->wait_for_stripe);
+       return handled;
+}
+
+
+
 /*
  * This is our raid5 kernel thread.
  *
@@ -3071,6 +3213,7 @@ static void raid5d (mddev_t *mddev)
        spin_lock_irq(&conf->device_lock);
        while (1) {
                struct list_head *first;
+               struct bio *bio;
 
                if (conf->seq_flush != conf->seq_write) {
                        int seq = conf->seq_flush;
@@ -3087,6 +3230,16 @@ static void raid5d (mddev_t *mddev)
                    !list_empty(&conf->delayed_list))
                        raid5_activate_delayed(conf);
 
+               while ((bio = remove_bio_from_retry(conf))) {
+                       int ok;
+                       spin_unlock_irq(&conf->device_lock);
+                       ok = retry_aligned_read(conf, bio);
+                       spin_lock_irq(&conf->device_lock);
+                       if (!ok)
+                               break;
+                       handled++;
+               }
+
                if (list_empty(&conf->handle_list))
                        break;
 
@@ -3274,6 +3427,7 @@ static int run(mddev_t *mddev)
        INIT_LIST_HEAD(&conf->inactive_list);
        atomic_set(&conf->active_stripes, 0);
        atomic_set(&conf->preread_active_stripes, 0);
+       atomic_set(&conf->active_aligned_reads, 0);
 
        PRINTK("raid5: run(%s) called.\n", mdname(mddev));
 
@@ -3796,7 +3950,8 @@ static void raid5_quiesce(mddev_t *mddev, int state)
                spin_lock_irq(&conf->device_lock);
                conf->quiesce = 1;
                wait_event_lock_irq(conf->wait_for_stripe,
-                                   atomic_read(&conf->active_stripes) == 0,
+                                   atomic_read(&conf->active_stripes) == 0 &&
+                                   atomic_read(&conf->active_aligned_reads) == 0,
                                    conf->device_lock, /* nothing */);
                spin_unlock_irq(&conf->device_lock);
                break;

diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index 03636d7..d8286db 100644 (file)
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -227,7 +227,10 @@ struct raid5_private_data {
        struct list_head        handle_list; /* stripes needing handling */
        struct list_head        delayed_list; /* stripes that have plugged requests */
        struct list_head        bitmap_list; /* stripes delaying awaiting bitmap update */
+       struct bio              *retry_read_aligned; /* currently retrying aligned bios   */
+       struct bio              *retry_read_aligned_list; /* aligned bios retry list  */
        atomic_t                preread_active_stripes; /* stripes with scheduled io */
+       atomic_t                active_aligned_reads;
 
        atomic_t                reshape_stripes; /* stripes with pending writes for reshape */
        /* unfortunately we need two cache names as we temporarily have