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Subject[125/139] md: deal with merge_bvec_fn in component devices better.
2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------
From: NeilBrown <neilb@suse.de>

commit 627a2d3c29427637f4c5d31ccc7fcbd8d312cd71 upstream.

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_phys_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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/md/linear.c | 12 +++++++-----
drivers/md/multipath.c | 20 ++++++++++++--------
drivers/md/raid0.c | 13 +++++++------
drivers/md/raid10.c | 28 +++++++++++++++++-----------
4 files changed, 43 insertions(+), 30 deletions(-)
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -172,12 +172,14 @@ static linear_conf_t *linear_conf(mddev_
disk_stack_limits(mddev->gendisk, rdev->bdev,
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_phys_segments to 1 lying within
+ * a single page.
*/
- if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
- queue_max_sectors(mddev->queue) > (PAGE_SIZE>>9))
- blk_queue_max_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
+ blk_queue_max_phys_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }

conf->array_sectors += rdev->sectors;
cnt++;
--- a/drivers/md/multipath.c
+++ b/drivers/md/multipath.c
@@ -301,14 +301,16 @@ static int multipath_add_disk(mddev_t *m
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_phys_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_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (q->merge_bvec_fn) {
+ blk_queue_max_phys_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }

conf->working_disks++;
mddev->degraded--;
@@ -476,9 +478,11 @@ static int multipath_run (mddev_t *mddev
/* 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_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
+ blk_queue_max_phys_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }

if (!test_bit(Faulty, &rdev->flags))
conf->working_disks++;
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -176,14 +176,15 @@ static int create_strip_zones(mddev_t *m
disk_stack_limits(mddev->gendisk, rdev1->bdev,
rdev1->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_phys_segments to 1, lying within
+ * a single page.
*/

- if (rdev1->bdev->bd_disk->queue->merge_bvec_fn &&
- queue_max_sectors(mddev->queue) > (PAGE_SIZE>>9))
- blk_queue_max_sectors(mddev->queue, PAGE_SIZE>>9);
-
+ if (rdev1->bdev->bd_disk->queue->merge_bvec_fn) {
+ blk_queue_max_phys_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }
if (!smallest || (rdev1->sectors < smallest->sectors))
smallest = rdev1;
cnt++;
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1155,13 +1155,17 @@ static int raid10_add_disk(mddev_t *mdde

disk_stack_limits(mddev->gendisk, rdev->bdev,
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.
+ /* as we don't honour merge_bvec_fn, we must
+ * never risk violating it, so limit
+ * ->max_phys_segments to one lying with a single
+ * page, as a one page request is never in
+ * violation.
*/
- if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
- queue_max_sectors(mddev->queue) > (PAGE_SIZE>>9))
- blk_queue_max_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
+ blk_queue_max_phys_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }

p->head_position = 0;
rdev->raid_disk = mirror;
@@ -2255,12 +2259,14 @@ static int run(mddev_t *mddev)
disk_stack_limits(mddev->gendisk, rdev->bdev,
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_phys_segments to 1 lying
+ * within a single page.
*/
- if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
- queue_max_sectors(mddev->queue) > (PAGE_SIZE>>9))
- blk_queue_max_sectors(mddev->queue, PAGE_SIZE>>9);
+ if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
+ blk_queue_max_phys_segments(mddev->queue, 1);
+ blk_queue_segment_boundary(mddev->queue,
+ PAGE_CACHE_SIZE - 1);
+ }

disk->head_position = 0;
}



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