genhd: Annotate all part and part_tbl pointer dereferences

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@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/genhd.c b/block/genhd.c
index 3dc4d11..2367087 100644 (file)
--- 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 fa5049a..1745a96 100644 (file)
--- 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);