From: Milan Broz <[email-masked]>

Fix setting of max_segment_size and seg_boundary mask for stacked md/dm devices.

When stacking devices (LVM over MD over SCSI) some of the request queue
parameters are not set up correctly in some cases by default, namely
max_segment_size and and seg_boundary mask.

If you create MD device over SCSI, these attributes are zeroed.

Problem become when there is over this mapping next device-mapper
mapping - queue attributes are set in DM this way:

request_queue   max_segment_size  seg_boundary_mask
SCSI                65536             0xffffffff
MD RAID1                0                      0
LVM                 65536                 -1 (64bit)

Unfortunately bio_add_page (resp. bio_phys_segments) calculates number
of physical segments according to these parameters.

During the generic_make_request() is segment cout recalculated and
can increase bio->bi_phys_segments count over the allowed limit.
(After bio_clone() in stack operation.)

Thi is specially problem in CCISS driver, where it produce OOPS here
    BUG_ON(creq->nr_phys_segments > MAXSGENTRIES);
(MAXSEGENTRIES is 31 by default.)

Sometimes even this command is enough to cause oops:
  dd iflag=direct if=/dev/<vg>/<lv> of=/dev/null bs=128000 count=10

This command generates bios with 250 sectors, allocated in 32 4k-pages
(last page uses only 1024 bytes).

For LVM layer, it allocates bio with 31 segments (still OK for CCISS),
unfortunatelly on lower layer it is recalculated to 32 segments and
this violates CCISS restriction and triggers BUG_ON().

Attached patch tries to fix it by:
 * initializing attributes above in queue request constructor
   blk_queue_make_request()

 * make sure that blk_queue_stack_limits() inherits setting

 (DM uses its own function to set the limits because
 it blk_queue_stack_limits() was introduced later.
 It should probably switch to use generic stack limit function too.)

 * sets the default seg_boundary value in one place (blkdev.h)

 * use this mask as default in DM (instead of -1, which differs in 64bit)

Bugs related to this:
https://bugzilla.redhat.com/show_bug.cgi?id=471639
http://bugzilla.kernel.org/show_bug.cgi?id=8672

Signed-off-by: Milan Broz <[email-masked]>
Signed-off-by: Alasdair G Kergon <[email-masked]>
---
 block/blk-core.c       |    2 +-
 block/blk-settings.c   |    4 ++++
 drivers/md/dm-table.c  |    2 +-
 include/linux/blkdev.h |    2 ++
 4 files changed, 8 insertions(+), 2 deletions(-)

Index: linux-2.6.28-rc7/block/blk-core.c
===================================================================
--- linux-2.6.28-rc7.orig/block/blk-core.c	2008-12-02 14:16:08.000000000 +0000
+++ linux-2.6.28-rc7/block/blk-core.c	2008-12-03 19:33:34.000000000 +0000
@@ -592,7 +592,7 @@ blk_init_queue_node(request_fn_proc *rfn
 				   1 << QUEUE_FLAG_STACKABLE);
 	q->queue_lock		= lock;
 
-	blk_queue_segment_boundary(q, 0xffffffff);
+	blk_queue_segment_boundary(q, BLK_SEG_BOUNDARY_MASK);
 
 	blk_queue_make_request(q, __make_request);
 	blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
Index: linux-2.6.28-rc7/block/blk-settings.c
===================================================================
--- linux-2.6.28-rc7.orig/block/blk-settings.c	2008-12-02 14:16:08.000000000 +0000
+++ linux-2.6.28-rc7/block/blk-settings.c	2008-12-03 19:33:34.000000000 +0000
@@ -125,6 +125,9 @@ void blk_queue_make_request(struct reque
 	q->nr_requests = BLKDEV_MAX_RQ;
 	blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
 	blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+	blk_queue_segment_boundary(q, BLK_SEG_BOUNDARY_MASK);
+	blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
+
 	q->make_request_fn = mfn;
 	q->backing_dev_info.ra_pages =
 			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
@@ -314,6 +317,7 @@ void blk_queue_stack_limits(struct reque
 	/* zero is "infinity" */
 	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
 	t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
+	t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask, b->seg_boundary_mask);
 
 	t->max_phys_segments = min(t->max_phys_segments, b->max_phys_segments);
 	t->max_hw_segments = min(t->max_hw_segments, b->max_hw_segments);
Index: linux-2.6.28-rc7/drivers/md/dm-table.c
===================================================================
--- linux-2.6.28-rc7.orig/drivers/md/dm-table.c	2008-12-03 19:33:19.000000000 +0000
+++ linux-2.6.28-rc7/drivers/md/dm-table.c	2008-12-03 19:33:34.000000000 +0000
@@ -688,7 +688,7 @@ static void check_for_valid_limits(struc
 	if (!rs->max_segment_size)
 		rs->max_segment_size = MAX_SEGMENT_SIZE;
 	if (!rs->seg_boundary_mask)
-		rs->seg_boundary_mask = -1;
+		rs->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
 	if (!rs->bounce_pfn)
 		rs->bounce_pfn = -1;
 }
Index: linux-2.6.28-rc7/include/linux/blkdev.h
===================================================================
--- linux-2.6.28-rc7.orig/include/linux/blkdev.h	2008-12-02 14:16:08.000000000 +0000
+++ linux-2.6.28-rc7/include/linux/blkdev.h	2008-12-03 19:33:34.000000000 +0000
@@ -921,6 +921,8 @@ extern void blk_set_cmd_filter_defaults(
 
 #define MAX_SEGMENT_SIZE	65536
 
+#define BLK_SEG_BOUNDARY_MASK	0xFFFFFFFFUL
+
 #define blkdev_entry_to_request(entry) list_entry((entry), struct request, queuelist)
 
 static inline int queue_hardsect_size(struct request_queue *q)