[PATCH 07/12] genhd: Annotate all part and part_tbl pointer dereferences

[Bart Van Assche <bart.vanassche@xxxxxxx>]

Annotate gendisk.part_tbl and disk_part_tbl.part dereferences with
rcu_dereference_protected(). This patch does not change the behavior
of the modified code but ensures that sparse does not complain about
disk->part_tbl manipulations nor about part_tbl->part accesses.
Additionally, improve documentation of the locking requirements of
the modified functions.

Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
---
 block/genhd.c             | 15 ++++++++++-----
 block/partition-generic.c | 15 ++++++++++++---
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 3dc4d115480f..2367087cdb7c 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1127,12 +1127,13 @@ static const struct attribute_group *disk_attr_groups[] = {
  * original ptbl is freed using RCU callback.
  *
  * LOCKING:
- * Matching bd_mutx locked.
+ * Matching bd_mutex locked or the caller is the only user of @disk.
  */
 static void disk_replace_part_tbl(struct gendisk *disk,
 				  struct disk_part_tbl *new_ptbl)
 {
-	struct disk_part_tbl *old_ptbl = disk->part_tbl;
+	struct disk_part_tbl *old_ptbl =
+		rcu_dereference_protected(disk->part_tbl, 1);
 
 	rcu_assign_pointer(disk->part_tbl, new_ptbl);
 
@@ -1151,14 +1152,16 @@ static void disk_replace_part_tbl(struct gendisk *disk,
  * uses RCU to allow unlocked dereferencing for stats and other stuff.
  *
  * LOCKING:
- * Matching bd_mutex locked, might sleep.
+ * Matching bd_mutex locked or the caller is the only user of @disk.
+ * Might sleep.
  *
  * RETURNS:
  * 0 on success, -errno on failure.
  */
 int disk_expand_part_tbl(struct gendisk *disk, int partno)
 {
-	struct disk_part_tbl *old_ptbl = disk->part_tbl;
+	struct disk_part_tbl *old_ptbl =
+		rcu_dereference_protected(disk->part_tbl, 1);
 	struct disk_part_tbl *new_ptbl;
 	int len = old_ptbl ? old_ptbl->len : 0;
 	int i, target;
@@ -1352,6 +1355,7 @@ EXPORT_SYMBOL(alloc_disk);
 struct gendisk *alloc_disk_node(int minors, int node_id)
 {
 	struct gendisk *disk;
+	struct disk_part_tbl *ptbl;
 
 	disk = kzalloc_node(sizeof(struct gendisk), GFP_KERNEL, node_id);
 	if (disk) {
@@ -1365,7 +1369,8 @@ struct gendisk *alloc_disk_node(int minors, int node_id)
 			kfree(disk);
 			return NULL;
 		}
-		disk->part_tbl->part[0] = &disk->part0;
+		ptbl = rcu_dereference_protected(disk->part_tbl, 1);
+		rcu_assign_pointer(ptbl->part[0], &disk->part0);
 
 		/*
 		 * set_capacity() and get_capacity() currently don't use
diff --git a/block/partition-generic.c b/block/partition-generic.c
index fa5049a4d99b..1745a9659517 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -252,15 +252,20 @@ void __delete_partition(struct percpu_ref *ref)
 	call_rcu(&part->rcu_head, delete_partition_rcu_cb);
 }
 
+/*
+ * Must be called either with bd_mutex held, before a disk can be opened or
+ * after all disk users are gone.
+ */
 void delete_partition(struct gendisk *disk, int partno)
 {
-	struct disk_part_tbl *ptbl = disk->part_tbl;
+	struct disk_part_tbl *ptbl =
+		rcu_dereference_protected(disk->part_tbl, 1);
 	struct hd_struct *part;
 
 	if (partno >= ptbl->len)
 		return;
 
-	part = ptbl->part[partno];
+	part = rcu_dereference_protected(ptbl->part[partno], 1);
 	if (!part)
 		return;
 
@@ -280,6 +285,10 @@ static ssize_t whole_disk_show(struct device *dev,
 static DEVICE_ATTR(whole_disk, S_IRUSR | S_IRGRP | S_IROTH,
 		   whole_disk_show, NULL);
 
+/*
+ * Must be called either with bd_mutex held, before a disk can be opened or
+ * after all disk users are gone.
+ */
 struct hd_struct *add_partition(struct gendisk *disk, int partno,
 				sector_t start, sector_t len, int flags,
 				struct partition_meta_info *info)
@@ -295,7 +304,7 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 	err = disk_expand_part_tbl(disk, partno);
 	if (err)
 		return ERR_PTR(err);
-	ptbl = disk->part_tbl;
+	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
 
 	if (ptbl->part[partno])
 		return ERR_PTR(-EBUSY);
-- 
2.14.0