[PATCH] block: fix RO partition with RW disk

[Junxiao Bi <junxiao.bi@xxxxxxxxxx>]

When md raid1 was used with imsm metadata, during the boot stage,
the raid device will first be set to readonly, then mdmon will set
it read-write later. When there were some partitions in this device,
the following race would make some partition left ro and fail to mount.

CPU 1:                                                 CPU 2:
add_partition()                                        set_disk_ro() //set disk RW
 //disk was RO, so partition set to RO
 p->policy = get_disk_ro(disk);
                                                        if (disk->part0.policy != flag) {
                                                            set_disk_ro_uevent(disk, flag);
                                                            // disk set to RW
                                                            disk->part0.policy = flag;
                                                        }
                                                        // set all exit partition to RW
                                                        while ((part = disk_part_iter_next(&piter)))
                                                            part->policy = flag;
 // this part was not yet added, so it was still RO
 rcu_assign_pointer(ptbl->part[partno], p);

Move RO status setting of partitions after they were added into partition
table and introduce a mutex to sync RO status between disk and partitions.

Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
---
 block/genhd.c             | 3 +++
 block/partition-generic.c | 5 ++++-
 include/linux/genhd.h     | 1 +
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index 54f1f0d381f4..f3cce1d354cf 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1479,6 +1479,7 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
 		}
 		ptbl = rcu_dereference_protected(disk->part_tbl, 1);
 		rcu_assign_pointer(ptbl->part[0], &disk->part0);
+		mutex_init(&disk->part_lock);
 
 		/*
 		 * set_capacity() and get_capacity() currently don't use
@@ -1570,6 +1571,7 @@ void set_disk_ro(struct gendisk *disk, int flag)
 	struct disk_part_iter piter;
 	struct hd_struct *part;
 
+	mutex_lock(&disk->part_lock);
 	if (disk->part0.policy != flag) {
 		set_disk_ro_uevent(disk, flag);
 		disk->part0.policy = flag;
@@ -1579,6 +1581,7 @@ void set_disk_ro(struct gendisk *disk, int flag)
 	while ((part = disk_part_iter_next(&piter)))
 		part->policy = flag;
 	disk_part_iter_exit(&piter);
+	mutex_unlock(&disk->part_lock);
 }
 
 EXPORT_SYMBOL(set_disk_ro);
diff --git a/block/partition-generic.c b/block/partition-generic.c
index aee643ce13d1..63cb6fb996ff 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -345,7 +345,6 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 		queue_limit_discard_alignment(&disk->queue->limits, start);
 	p->nr_sects = len;
 	p->partno = partno;
-	p->policy = get_disk_ro(disk);
 
 	if (info) {
 		struct partition_meta_info *pinfo = alloc_part_info(disk);
@@ -401,6 +400,10 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	/* everything is up and running, commence */
 	rcu_assign_pointer(ptbl->part[partno], p);
 
+	mutex_lock(&disk->part_lock);
+	p->policy = get_disk_ro(disk);
+	mutex_unlock(&disk->part_lock);
+
 	/* suppress uevent if the disk suppresses it */
 	if (!dev_get_uevent_suppress(ddev))
 		kobject_uevent(&pdev->kobj, KOBJ_ADD);
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 8b5330dd5ac0..df6ddca8a92c 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -201,6 +201,7 @@ struct gendisk {
 	 */
 	struct disk_part_tbl __rcu *part_tbl;
 	struct hd_struct part0;
+	struct mutex part_lock;
 
 	const struct block_device_operations *fops;
 	struct request_queue *queue;
-- 
2.17.1