From: Milan Broz 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 Cc: stable@kernel.org Acked-by: Mike Snitzer Signed-off-by: Alasdair G Kergon --- drivers/md/dm-io.c | 26 +++++++++++++++++++------- drivers/md/dm-io.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) Index: linux-3.3-rc6/drivers/md/dm-io.c =================================================================== --- linux-3.3-rc6.orig/drivers/md/dm-io.c +++ linux-3.3-rc6/drivers/md/dm-io.c @@ -296,6 +296,8 @@ static void do_region(int rw, unsigned r 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 r /* * 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 r 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))