md: deal with merge_bvec_fn in component devices better.
If a component device has a merge_bvec_fn then as we never call it
we must ensure we never need to. Currently this is done by setting
max_sector to 1 PAGE, however this does not stop a bio being created
with several sub-page iovecs that would violate the merge_bvec_fn.
So instead set max_segments to 1 and set the segment boundary to the
same as a page boundary to ensure there is only ever one single-page
segment of IO requested at a time.
This can particularly be an issue when 'xen' is used as it is
known to submit multiple small buffers in a single bio.
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
diff --git a/drivers/md/multipath.c b/drivers/md/multipath.c
index 4b323f4..5558ebc 100644
--- a/drivers/md/multipath.c
+++ b/drivers/md/multipath.c
@@ -301,14 +301,16 @@
rdev->data_offset << 9);
/* as we don't honour merge_bvec_fn, we must never risk
- * violating it, so limit ->max_sector to one PAGE, as
- * a one page request is never in violation.
+ * violating it, so limit ->max_segments to one, lying
+ * within a single page.
* (Note: it is very unlikely that a device with
* merge_bvec_fn will be involved in multipath.)
*/
- if (q->merge_bvec_fn &&
- queue_max_sectors(q) > (PAGE_SIZE>>9))
- blk_queue_max_hw_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (q->merge_bvec_fn) {
+ blk_queue_max_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }
conf->working_disks++;
mddev->degraded--;
@@ -476,9 +478,11 @@
/* as we don't honour merge_bvec_fn, we must never risk
* violating it, not that we ever expect a device with
* a merge_bvec_fn to be involved in multipath */
- if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
- queue_max_sectors(mddev->queue) > (PAGE_SIZE>>9))
- blk_queue_max_hw_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
+ blk_queue_max_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }
if (!test_bit(Faulty, &rdev->flags))
conf->working_disks++;