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Commit 0c535e0d authored by Milan Broz's avatar Milan Broz Committed by Alasdair G Kergon
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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 5fc2ffea
(dm raid1: support discard).

Signed-off-by: default avatarMilan Broz <mbroz@redhat.com>
Cc: stable@kernel.org
Acked-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 902c6a96

drivers/md/dm-io.c

+16 −7
Original line number Diff line number Diff line
@@ -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);



		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.

			 */

		while (remaining) {

			dp->get_page(dp, &page, &len, &offset);

			len = min(len, to_bytes(remaining));

			if (!bio_add_page(bio, page, len, offset))