dm io: fix discard support

This patch fixes a crash by recognising discards in dm_io.

Currently dm_mirror can send REQ_DISCARD bios if running over a
discard-enabled device and without support in dm_io the system
crashes badly.

BUG: unable to handle kernel paging request at 00800000
IP:  __bio_add_page.part.17+0xf5/0x1e0
...
 bio_add_page+0x56/0x70
 dispatch_io+0x1cf/0x240 [dm_mod]
 ? km_get_page+0x50/0x50 [dm_mod]
 ? vm_next_page+0x20/0x20 [dm_mod]
 ? mirror_flush+0x130/0x130 [dm_mirror]
 dm_io+0xdc/0x2b0 [dm_mod]
...

Introduced in 2.6.38-rc1 by commit 5fc2ffeabb9ee0fc0e71ff16b49f34f0ed3d05b4
(dm raid1: support discard).

Signed-off-by: Milan Broz <mbroz@redhat.com>
Cc: stable@kernel.org
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index ad2eba4..ea5dd28 100644 (file)
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -296,6 +296,8 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
        unsigned offset;
        unsigned num_bvecs;
        sector_t remaining = where->count;
+       struct request_queue *q = bdev_get_queue(where->bdev);
+       sector_t discard_sectors;
 
        /*
         * where->count may be zero if rw holds a flush and we need to
@@ -305,9 +307,12 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
                /*
                 * Allocate a suitably sized-bio.
                 */
-               num_bvecs = dm_sector_div_up(remaining,
-                                            (PAGE_SIZE >> SECTOR_SHIFT));
-               num_bvecs = min_t(int, bio_get_nr_vecs(where->bdev), num_bvecs);
+               if (rw & REQ_DISCARD)
+                       num_bvecs = 1;
+               else
+                       num_bvecs = min_t(int, bio_get_nr_vecs(where->bdev),
+                                         dm_sector_div_up(remaining, (PAGE_SIZE >> SECTOR_SHIFT)));
+
                bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
                bio->bi_sector = where->sector + (where->count - remaining);
                bio->bi_bdev = where->bdev;
@@ -315,10 +320,14 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
                bio->bi_destructor = dm_bio_destructor;
                store_io_and_region_in_bio(bio, io, region);
 
-               /*
-                * Try and add as many pages as possible.
-                */
-               while (remaining) {
+               if (rw & REQ_DISCARD) {
+                       discard_sectors = min_t(sector_t, q->limits.max_discard_sectors, remaining);
+                       bio->bi_size = discard_sectors << SECTOR_SHIFT;
+                       remaining -= discard_sectors;
+               } else while (remaining) {
+                       /*
+                        * Try and add as many pages as possible.
+                        */
                        dp->get_page(dp, &page, &len, &offset);
                        len = min(len, to_bytes(remaining));
                        if (!bio_add_page(bio, page, len, offset))