[PATCH] hugetlbfs: fix memory leak for resv_map

[Yufen Yu <yuyufen@huawei.com>]

When .mknod create a block device file in hugetlbfs, it will
allocate an inode, and kmalloc a 'struct resv_map' in resv_map_alloc().
For now, inode->i_mapping->private_data is used to point the resv_map.
However, when open the device, bd_acquire() will set i_mapping as
bd_inode->imapping, result in resv_map memory leak.

We fix the leak by adding a new entry resv_map in hugetlbfs_inode_info.
It can store resv_map pointer.

Programs to reproduce:
	mount -t hugetlbfs nodev hugetlbfs
	mknod hugetlbfs/dev b 0 0
	exec 30<> hugetlbfs/dev
	umount hugetlbfs/

Fixes: 9119a41e90 ("mm, hugetlb: unify region structure handling")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
---
 fs/hugetlbfs/inode.c    | 12 +++++++++---
 include/linux/hugetlb.h |  1 +
 mm/hugetlb.c            |  2 +-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index a7fa037b876b..7f332443c5da 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -484,11 +484,15 @@ static void hugetlbfs_evict_inode(struct inode *inode)
 {
 	struct resv_map *resv_map;
 
+	struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
+
 	remove_inode_hugepages(inode, 0, LLONG_MAX);
-	resv_map = (struct resv_map *)inode->i_mapping->private_data;
+	resv_map = info->resv_map;
 	/* root inode doesn't have the resv_map, so we should check it */
-	if (resv_map)
+	if (resv_map) {
 		resv_map_release(&resv_map->refs);
+		info->resv_map = NULL;
+	}
 	clear_inode(inode);
 }
 
@@ -757,7 +761,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
 				&hugetlbfs_i_mmap_rwsem_key);
 		inode->i_mapping->a_ops = &hugetlbfs_aops;
 		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
-		inode->i_mapping->private_data = resv_map;
+		info->resv_map = resv_map;
 		info->seals = F_SEAL_SEAL;
 		switch (mode & S_IFMT) {
 		default:
@@ -1025,6 +1029,7 @@ static struct inode *hugetlbfs_alloc_inode(struct super_block *sb)
 	 * private inode.  This simplifies hugetlbfs_destroy_inode.
 	 */
 	mpol_shared_policy_init(&p->policy, NULL);
+	p->resv_map = NULL;
 
 	return &p->vfs_inode;
 }
@@ -1039,6 +1044,7 @@ static void hugetlbfs_destroy_inode(struct inode *inode)
 {
 	hugetlbfs_inc_free_inodes(HUGETLBFS_SB(inode->i_sb));
 	mpol_free_shared_policy(&HUGETLBFS_I(inode)->policy);
+	HUGETLBFS_I(inode)->resv_map = NULL;
 	call_rcu(&inode->i_rcu, hugetlbfs_i_callback);
 }
 
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 087fd5f48c91..eafcf14056bc 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -291,6 +291,7 @@ struct hugetlbfs_inode_info {
 	struct shared_policy policy;
 	struct inode vfs_inode;
 	unsigned int seals;
+	struct resv_map *resv_map;
 };
 
 static inline struct hugetlbfs_inode_info *HUGETLBFS_I(struct inode *inode)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8dfdffc34a99..763164b15f8f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -739,7 +739,7 @@ void resv_map_release(struct kref *ref)
 
 static inline struct resv_map *inode_resv_map(struct inode *inode)
 {
-	return inode->i_mapping->private_data;
+	return HUGETLBFS_I(inode)->resv_map;
 }
 
 static struct resv_map *vma_resv_map(struct vm_area_struct *vma)
-- 
2.16.2.dirty