md/linear: remove rcu protections in favour of suspend/resume

The use of 'rcu' to protect accesses to ->private_data so that
the ->private_data could be updated predates the introduction
of mddev_suspend/mddev_resume.
These are a cleaner mechanism for providing stability while
swapping in a new ->private data - it is used by level_store()
to support changing of raid levels.

So get rid of the RCU stuff and just use mddev_suspend, mddev_resume.

As these function call ->quiesce(), we add an empty function for
linear just like for raid0.

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

1 files changed, 14 insertions, 30 deletions

diff --git a/drivers/md/linear.c b/drivers/md/linear.c
index 4c2a92ce2b0b..b3e717adbc9b 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -34,7 +34,7 @@ static inline struct dev_info *which_dev(struct mddev *mddev, sector_t sector)
 
         lo = 0;
         hi = mddev->raid_disks - 1;
-        conf = rcu_dereference(mddev->private);
+        conf = mddev->private;
 
         /*
          * Binary Search
@@ -70,7 +70,6 @@ static int linear_mergeable_bvec(struct mddev *mddev,
         int maxbytes = biovec->bv_len;
         struct request_queue *subq;
 
-        rcu_read_lock();
         dev0 = which_dev(mddev, sector);
         maxsectors = dev0->end_sector - sector;
         subq = bdev_get_queue(dev0->rdev->bdev);
@@ -80,7 +79,6 @@ static int linear_mergeable_bvec(struct mddev *mddev,
                 maxbytes = min(maxbytes, subq->merge_bvec_fn(subq, bvm,
                                                              biovec));
         }
-        rcu_read_unlock();
 
         if (maxsectors < bio_sectors)
                 maxsectors = 0;
@@ -101,15 +99,13 @@ static int linear_congested(struct mddev *mddev, int bits)
         struct linear_conf *conf;
         int i, ret = 0;
 
-        rcu_read_lock();
-        conf = rcu_dereference(mddev->private);
+        conf = mddev->private;
 
         for (i = 0; i < mddev->raid_disks && !ret ; i++) {
                 struct request_queue *q = bdev_get_queue(conf->disks[i].rdev->bdev);
                 ret |= bdi_congested(&q->backing_dev_info, bits);
         }
 
-        rcu_read_unlock();
         return ret;
 }
 
@@ -118,12 +114,10 @@ static sector_t linear_size(struct mddev *mddev, sector_t sectors, int raid_disk
         struct linear_conf *conf;
         sector_t array_sectors;
 
-        rcu_read_lock();
-        conf = rcu_dereference(mddev->private);
+        conf = mddev->private;
         WARN_ONCE(sectors || raid_disks,
                   "%s does not support generic reshape\n", __func__);
         array_sectors = conf->array_sectors;
-        rcu_read_unlock();
 
         return array_sectors;
 }
@@ -243,33 +237,22 @@ static int linear_add(struct mddev *mddev, struct md_rdev *rdev)
         if (!newconf)
                 return -ENOMEM;
 
-        oldconf = rcu_dereference_protected(mddev->private,
-                                            lockdep_is_held(
-                                                    &mddev->reconfig_mutex));
+        mddev_suspend(mddev);
+        oldconf = mddev->private;
         mddev->raid_disks++;
-        rcu_assign_pointer(mddev->private, newconf);
+        mddev->private = newconf;
         md_set_array_sectors(mddev, linear_size(mddev, 0, 0));
         set_capacity(mddev->gendisk, mddev->array_sectors);
+        mddev_resume(mddev);
         revalidate_disk(mddev->gendisk);
-        kfree_rcu(oldconf, rcu);
+        kfree(oldconf);
         return 0;
 }
 
 static int linear_stop (struct mddev *mddev)
 {
-        struct linear_conf *conf =
-                rcu_dereference_protected(mddev->private,
-                                          lockdep_is_held(
-                                                  &mddev->reconfig_mutex));
+        struct linear_conf *conf = mddev->private;
 
-        /*
-         * We do not require rcu protection here since
-         * we hold reconfig_mutex for both linear_add and
-         * linear_stop, so they cannot race.
-         * We should make sure any old 'conf's are properly
-         * freed though.
-         */
-        rcu_barrier();
         blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
         kfree(conf);
         mddev->private = NULL;
@@ -290,16 +273,12 @@ static void linear_make_request(struct mddev *mddev, struct bio *bio)
         }
 
         do {
-                rcu_read_lock();
-
                 tmp_dev = which_dev(mddev, bio->bi_iter.bi_sector);
                 start_sector = tmp_dev->end_sector - tmp_dev->rdev->sectors;
                 end_sector = tmp_dev->end_sector;
                 data_offset = tmp_dev->rdev->data_offset;
                 bio->bi_bdev = tmp_dev->rdev->bdev;
 
-                rcu_read_unlock();
-
                 if (unlikely(bio->bi_iter.bi_sector >= end_sector ||
                              bio->bi_iter.bi_sector < start_sector))
                         goto out_of_bounds;
@@ -346,6 +325,10 @@ static void linear_status (struct seq_file *seq, struct mddev *mddev)
         seq_printf(seq, " %dk rounding", mddev->chunk_sectors / 2);
 }
 
+static void linear_quiesce(struct mddev *mddev, int state)
+{
+}
+
 static struct md_personality linear_personality =
 {
         .name           = "linear",
@@ -357,6 +340,7 @@ static struct md_personality linear_personality =
         .status         = linear_status,
         .hot_add_disk   = linear_add,
         .size           = linear_size,
+        .quiesce        = linear_quiesce,
         .congested      = linear_congested,
         .mergeable_bvec = linear_mergeable_bvec,
 };