From 8cbeb67ad50f7d68e5e83be2cb2284de8f9c03b5 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 22 Jun 2009 10:12:14 +0100 Subject: dm: avoid unsupported spanning of md stripe boundaries A bio that has two or more vector entries, size less than or equal to page size, that crosses a stripe boundary of an underlying md device is accepted by device mapper (it conforms to all its limits) but not by the underlying device. The fix is: If device mapper selects the one-page maximum request size, it also needs to set its own q->merge_bvec_fn to reject any bios with multiple vector entries that span more pages. The problem was discovered in the following scenario: * MD - RAID-0 * LV on the top of it (raid1, snapshot or striped with chunk size/stripe larger than RAID-0 stripe) * one of the logical volumes is exported to xen domU * inside xen domU it is partitioned, the key point is that the partition must be unaligned on page boundary (fdisk normally aligns the partition to 63 sectors which will trigger it) * install the system on the partitioned disk in domU This causes I/O failures in dom0. Reference: https://bugzilla.redhat.com/show_bug.cgi?id=223947 Signed-off-by: Mikulas Patocka Signed-off-by: Alasdair G Kergon --- drivers/md/dm.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'drivers/md') diff --git a/drivers/md/dm.c b/drivers/md/dm.c index f1db689667ea..59806e67a175 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -925,6 +925,16 @@ static int dm_merge_bvec(struct request_queue *q, */ if (max_size && ti->type->merge) max_size = ti->type->merge(ti, bvm, biovec, max_size); + /* + * If the target doesn't support merge method and some of the devices + * provided their merge_bvec method (we know this by looking at + * queue_max_hw_sectors), then we can't allow bios with multiple vector + * entries. So always set max_size to 0, and the code below allows + * just one page. + */ + else if (queue_max_hw_sectors(q) <= PAGE_SIZE >> 9) + + max_size = 0; out_table: dm_table_put(map); -- cgit v1.2.3