From: Milan Broz <mbroz@redhat.com>
Subject: [RHEL5.1 PATCH] dm io: fix panic on large request
Date: Wed, 23 May 2007 13:58:17 +0200
Bugzilla: 240751
Message-Id: <46542C59.9040308@redhat.com>
Changelog: [md] dm io: fix panic on large request


RHEL5.1 dm io: panic on large request
Resolves: rhbz#240751
Patch is upstream in -mm tree.

When creating large (>6TB) dm/lvm mirror volume, 
bio_alloc_bioset() will return NULL ('num_vecs' is too large).

Fix by use bio_get_nr_vecs() to get estimation of maximum number.

Tested with simulated big mirror creation request
(reproducer script on bugzilla).

---
 drivers/md/dm-io.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-2.6.18/drivers/md/dm-io.c
===================================================================
--- linux-2.6.18.orig/drivers/md/dm-io.c	2007-05-21 15:53:01.000000000 +0200
+++ linux-2.6.18/drivers/md/dm-io.c	2007-05-21 16:21:33.000000000 +0200
@@ -357,7 +357,9 @@ static void do_region(int rw, unsigned i
 		 * bvec for bio_get/set_region() and decrement bi_max_vecs
 		 * to hide it from bio_add_page().
 		 */
-		num_bvecs = (remaining / (PAGE_SIZE >> SECTOR_SHIFT)) + 2;
+		num_bvecs = dm_div_up(remaining, (PAGE_SIZE >> SECTOR_SHIFT));
+		num_bvecs = 1 + min_t(int, bio_get_nr_vecs(where->bdev),
+				      num_bvecs);
 		bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, bios(io->client));
 		bio->bi_sector = where->sector + (where->count - remaining);
 		bio->bi_bdev = where->bdev;