md/raid1: handle merge_bvec_fn in member devices.

Currently we don't honour merge_bvec_fn in member devices so if there
is one, we force all requests to be single-page at most.
This is not ideal.

So create a raid1 merge_bvec_fn to check that function in children
as well.

This introduces a small problem.  There is no locking around calls
the ->merge_bvec_fn and subsequent calls to ->make_request.  So a
device added between these could end up getting a request which
violates its merge_bvec_fn.

Currently the best we can do is synchronize_sched().  This will work
providing no preemption happens.  If there is is preemption, we just
have to hope that new devices are largely consistent with old devices.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 56 insertions, 21 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index a933bd4065a..4a40a200d76 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -523,6 +523,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                 rdev = rcu_dereference(conf->mirrors[disk].rdev);
                 if (r1_bio->bios[disk] == IO_BLOCKED
                     || rdev == NULL
+                    || test_bit(Unmerged, &rdev->flags)
                     || test_bit(Faulty, &rdev->flags))
                         continue;
                 if (!test_bit(In_sync, &rdev->flags) &&
@@ -614,6 +615,39 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
         return best_disk;
 }
 
+static int raid1_mergeable_bvec(struct request_queue *q,
+                                struct bvec_merge_data *bvm,
+                                struct bio_vec *biovec)
+{
+        struct mddev *mddev = q->queuedata;
+        struct r1conf *conf = mddev->private;
+        sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
+        int max = biovec->bv_len;
+
+        if (mddev->merge_check_needed) {
+                int disk;
+                rcu_read_lock();
+                for (disk = 0; disk < conf->raid_disks * 2; disk++) {
+                        struct md_rdev *rdev = rcu_dereference(
+                                conf->mirrors[disk].rdev);
+                        if (rdev && !test_bit(Faulty, &rdev->flags)) {
+                                struct request_queue *q =
+                                        bdev_get_queue(rdev->bdev);
+                                if (q->merge_bvec_fn) {
+                                        bvm->bi_sector = sector +
+                                                rdev->data_offset;
+                                        bvm->bi_bdev = rdev->bdev;
+                                        max = min(max, q->merge_bvec_fn(
+                                                          q, bvm, biovec));
+                                }
+                        }
+                }
+                rcu_read_unlock();
+        }
+        return max;
+
+}
+
 int md_raid1_congested(struct mddev *mddev, int bits)
 {
         struct r1conf *conf = mddev->private;
@@ -1015,7 +1049,8 @@ read_again:
                         break;
                 }
                 r1_bio->bios[i] = NULL;
-                if (!rdev || test_bit(Faulty, &rdev->flags)) {
+                if (!rdev || test_bit(Faulty, &rdev->flags)
+                    || test_bit(Unmerged, &rdev->flags)) {
                         if (i < conf->raid_disks)
                                 set_bit(R1BIO_Degraded, &r1_bio->state);
                         continue;
@@ -1335,6 +1370,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
         struct mirror_info *p;
         int first = 0;
         int last = conf->raid_disks - 1;
+        struct request_queue *q = bdev_get_queue(rdev->bdev);
 
         if (mddev->recovery_disabled == conf->recovery_disabled)
                 return -EBUSY;
@@ -1342,23 +1378,17 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
         if (rdev->raid_disk >= 0)
                 first = last = rdev->raid_disk;
 
+        if (q->merge_bvec_fn) {
+                set_bit(Unmerged, &rdev->flags);
+                mddev->merge_check_needed = 1;
+        }
+
         for (mirror = first; mirror <= last; mirror++) {
                 p = conf->mirrors+mirror;
                 if (!p->rdev) {
 
                         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_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) {
-                                blk_queue_max_segments(mddev->queue, 1);
-                                blk_queue_segment_boundary(mddev->queue,
-                                                           PAGE_CACHE_SIZE - 1);
-                        }
 
                         p->head_position = 0;
                         rdev->raid_disk = mirror;
@@ -1383,6 +1413,19 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
                         break;
                 }
         }
+        if (err == 0 && test_bit(Unmerged, &rdev->flags)) {
+                /* Some requests might not have seen this new
+                 * merge_bvec_fn.  We must wait for them to complete
+                 * before merging the device fully.
+                 * First we make sure any code which has tested
+                 * our function has submitted the request, then
+                 * we wait for all outstanding requests to complete.
+                 */
+                synchronize_sched();
+                raise_barrier(conf);
+                lower_barrier(conf);
+                clear_bit(Unmerged, &rdev->flags);
+        }
         md_integrity_add_rdev(rdev, mddev);
         print_conf(conf);
         return err;
@@ -2627,15 +2670,6 @@ static int run(struct mddev *mddev)
                         continue;
                 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_segments to 1 lying within
-                 * a single page, as a one page request is never in violation.
-                 */
-                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);
-                }
         }
 
         mddev->degraded = 0;
@@ -2669,6 +2703,7 @@ static int run(struct mddev *mddev)
         if (mddev->queue) {
                 mddev->queue->backing_dev_info.congested_fn = raid1_congested;
                 mddev->queue->backing_dev_info.congested_data = mddev;
+                blk_queue_merge_bvec(mddev->queue, raid1_mergeable_bvec);
         }
         return md_integrity_register(mddev);
 }