[PATCH] md: fix various bugs with aligned reads in RAID5

It is possible for raid5 to be sent a bio that is too big for an underlying
device.  So if it is a READ that we pass stright down to a device, it will
fail and confuse RAID5.

So in 'chunk_aligned_read' we check that the bio fits within the parameters
for the target device and if it doesn't fit, fall back on reading through
the stripe cache and making lots of one-page requests.

Note that this is the earliest time we can check against the device because
earlier we don't have a lock on the device, so it could change underneath
us.

Also, the code for handling a retry through the cache when a read fails has
not been tested and was badly broken.  This patch fixes that code.

Signed-off-by: Neil Brown <neilb@suse.de>
Cc: "Kai" <epimetreus@fastmail.fm>
Cc: <stable@suse.de>
Cc: <org@suse.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 40 insertions, 4 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index fb6789725e1b..38c293b987b7 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1264,7 +1264,7 @@ new_hw_segment:
         bio->bi_hw_segments = nr_hw_segs;
         bio->bi_flags |= (1 << BIO_SEG_VALID);
 }
-
+EXPORT_SYMBOL(blk_recount_segments);
 
 static int blk_phys_contig_segment(request_queue_t *q, struct bio *bio,
                                    struct bio *nxt)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 467c16982d02..11c3d7bfa797 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2620,7 +2620,7 @@ static struct bio *remove_bio_from_retry(raid5_conf_t *conf)
         }
         bi = conf->retry_read_aligned_list;
         if(bi) {
-                conf->retry_read_aligned = bi->bi_next;
+                conf->retry_read_aligned_list = 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 */
@@ -2669,6 +2669,27 @@ static int raid5_align_endio(struct bio *bi, unsigned int bytes, int error)
         return 0;
 }
 
+static int bio_fits_rdev(struct bio *bi)
+{
+        request_queue_t *q = bdev_get_queue(bi->bi_bdev);
+
+        if ((bi->bi_size>>9) > q->max_sectors)
+                return 0;
+        blk_recount_segments(q, bi);
+        if (bi->bi_phys_segments > q->max_phys_segments ||
+            bi->bi_hw_segments > q->max_hw_segments)
+                return 0;
+
+        if (q->merge_bvec_fn)
+                /* it's too hard to apply the merge_bvec_fn at this stage,
+                 * just just give up
+                 */
+                return 0;
+
+        return 1;
+}
+
+
 static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
 {
         mddev_t *mddev = q->queuedata;
@@ -2715,6 +2736,13 @@ static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
                 align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
                 align_bi->bi_sector += rdev->data_offset;
 
+                if (!bio_fits_rdev(align_bi)) {
+                        /* too big in some way */
+                        bio_put(align_bi);
+                        rdev_dec_pending(rdev, mddev);
+                        return 0;
+                }
+
                 spin_lock_irq(&conf->device_lock);
                 wait_event_lock_irq(conf->wait_for_stripe,
                                     conf->quiesce == 0,
@@ -3107,7 +3135,9 @@ static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
         last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);
 
         for (; logical_sector < last_sector;
-             logical_sector += STRIPE_SECTORS, scnt++) {
+             logical_sector += STRIPE_SECTORS,
+                     sector += STRIPE_SECTORS,
+                     scnt++) {
 
                 if (scnt < raid_bio->bi_hw_segments)
                         /* already done this stripe */
@@ -3123,7 +3153,13 @@ static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
                 }
 
                 set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
-                add_stripe_bio(sh, raid_bio, dd_idx, 0);
+                if (!add_stripe_bio(sh, raid_bio, dd_idx, 0)) {
+                        release_stripe(sh);
+                        raid_bio->bi_hw_segments = scnt;
+                        conf->retry_read_aligned = raid_bio;
+                        return handled;
+                }
+
                 handle_stripe(sh, NULL);
                 release_stripe(sh);
                 handled++;