[PATCH 2/4] block: only define 'nr_sects_seq' in hd_part for 32bit SMP

[Ming Lei <ming.lei@redhat.com>]

The seqcount of 'nr_sects_seq' is only needed in case of 32bit SMP,
so define it just for 32bit SMP.

Cc: Yufen Yu <yuyufen@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hou Tao <houtao1@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/genhd.c             | 2 +-
 block/partition-generic.c | 2 +-
 include/linux/genhd.h     | 9 +++++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 6029c94510f0..bfc4148ec341 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1506,7 +1506,7 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
 		 * TODO: Ideally set_capacity() and get_capacity() should be
 		 * converted to make use of bd_mutex and sequence counters.
 		 */
-		seqcount_init(&disk->part0.nr_sects_seq);
+		hd_sects_seq_init(&disk->part0);
 		if (hd_ref_init(&disk->part0)) {
 			hd_free_part(&disk->part0);
 			kfree(disk);
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 1739f750dbf2..eb606c2c3d6c 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -345,7 +345,7 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 		goto out_free;
 	}
 
-	seqcount_init(&p->nr_sects_seq);
+	hd_sects_seq_init(p);
 	pdev = part_to_dev(p);
 
 	p->start_sect = start;
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 1b09cfe00aa3..5f5718ce5e86 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -113,7 +113,9 @@ struct hd_struct {
 	 * can be non-atomic on 32bit machines with 64bit sector_t.
 	 */
 	sector_t nr_sects;
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
 	seqcount_t nr_sects_seq;
+#endif
 	sector_t alignment_offset;
 	unsigned int discard_alignment;
 	struct device __dev;
@@ -713,6 +715,13 @@ static inline void hd_free_part(struct hd_struct *part)
 	percpu_ref_exit(&part->ref);
 }
 
+static inline void hd_sects_seq_init(struct hd_struct *p)
+{
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+	seqcount_init(&p->nr_sects_seq);
+#endif
+}
+
 /*
  * Any access of part->nr_sects which is not protected by partition
  * bd_mutex or gendisk bdev bd_mutex, should be done using this
-- 
2.20.1