1 files changed, 28 insertions, 13 deletions

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2b461b496a78..19cc761cacb2 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -44,6 +44,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         struct request_queue *q = bdev_get_queue(bdev);
         int type = REQ_WRITE | REQ_DISCARD;
         unsigned int max_discard_sectors;
+        unsigned int granularity, alignment, mask;
         struct bio_batch bb;
         struct bio *bio;
         int ret = 0;
@@ -54,18 +55,20 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         if (!blk_queue_discard(q))
                 return -EOPNOTSUPP;
 
+        /* Zero-sector (unknown) and one-sector granularities are the same.  */
+        granularity = max(q->limits.discard_granularity >> 9, 1U);
+        mask = granularity - 1;
+        alignment = (bdev_discard_alignment(bdev) >> 9) & mask;
+
         /*
          * Ensure that max_discard_sectors is of the proper
-         * granularity
+         * granularity, so that requests stay aligned after a split.
          */
         max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
+        max_discard_sectors = round_down(max_discard_sectors, granularity);
         if (unlikely(!max_discard_sectors)) {
                 /* Avoid infinite loop below. Being cautious never hurts. */
                 return -EOPNOTSUPP;
-        } else if (q->limits.discard_granularity) {
-                unsigned int disc_sects = q->limits.discard_granularity >> 9;
-
-                max_discard_sectors &= ~(disc_sects - 1);
         }
 
         if (flags & BLKDEV_DISCARD_SECURE) {
@@ -79,25 +82,37 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         bb.wait = &wait;
 
         while (nr_sects) {
+                unsigned int req_sects;
+                sector_t end_sect;
+
                 bio = bio_alloc(gfp_mask, 1);
                 if (!bio) {
                         ret = -ENOMEM;
                         break;
                 }
 
+                req_sects = min_t(sector_t, nr_sects, max_discard_sectors);
+
+                /*
+                 * If splitting a request, and the next starting sector would be
+                 * misaligned, stop the discard at the previous aligned sector.
+                 */
+                end_sect = sector + req_sects;
+                if (req_sects < nr_sects && (end_sect & mask) != alignment) {
+                        end_sect =
+                                round_down(end_sect - alignment, granularity)
+                                + alignment;
+                        req_sects = end_sect - sector;
+                }
+
                 bio->bi_sector = sector;
                 bio->bi_end_io = bio_batch_end_io;
                 bio->bi_bdev = bdev;
                 bio->bi_private = &bb;
 
-                if (nr_sects > max_discard_sectors) {
-                        bio->bi_size = max_discard_sectors << 9;
-                        nr_sects -= max_discard_sectors;
-                        sector += max_discard_sectors;
-                } else {
-                        bio->bi_size = nr_sects << 9;
-                        nr_sects = 0;
-                }
+                bio->bi_size = req_sects << 9;
+                nr_sects -= req_sects;
+                sector = end_sect;
 
                 atomic_inc(&bb.done);
                 submit_bio(type, bio);