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Subject[PATCH] hugetlbfs: always use address space in inode for resv_map pointer
Date
Continuing discussion about commit 58b6e5e8f1ad ("hugetlbfs: fix memory
leak for resv_map") brought up the issue that inode->i_mapping may not
point to the address space embedded within the inode at inode eviction
time. The hugetlbfs truncate routine handles this by explicitly using
inode->i_data. However, code cleaning up the resv_map will still use
the address space pointed to by inode->i_mapping. Luckily, private_data
is NULL for address spaces in all such cases today but, there is no
guarantee this will continue.

Change all hugetlbfs code getting a resv_map pointer to explicitly get
it from the address space embedded within the inode. In addition, add
more comments in the code to indicate why this is being done.

Reported-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
fs/hugetlbfs/inode.c | 11 +++++++++--
mm/hugetlb.c | 19 ++++++++++++++++++-
2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9285dd4f4b1c..cbc649cd1722 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -499,8 +499,15 @@ static void hugetlbfs_evict_inode(struct inode *inode)
struct resv_map *resv_map;

remove_inode_hugepages(inode, 0, LLONG_MAX);
- resv_map = (struct resv_map *)inode->i_mapping->private_data;
- /* root inode doesn't have the resv_map, so we should check it */
+
+ /*
+ * Get the resv_map from the address space embedded in the inode.
+ * This is the address space which points to any resv_map allocated
+ * at inode creation time. If this is a device special inode,
+ * i_mapping may not point to the original address space.
+ */
+ resv_map = (struct resv_map *)(&inode->i_data)->private_data;
+ /* Only regular and link inodes have associated reserve maps */
if (resv_map)
resv_map_release(&resv_map->refs);
clear_inode(inode);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6cdc7b2d9100..b30e97b0ef37 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -740,7 +740,15 @@ void resv_map_release(struct kref *ref)

static inline struct resv_map *inode_resv_map(struct inode *inode)
{
- return inode->i_mapping->private_data;
+ /*
+ * At inode evict time, i_mapping may not point to the original
+ * address space within the inode. This original address space
+ * contains the pointer to the resv_map. So, always use the
+ * address space embedded within the inode.
+ * The VERY common case is inode->mapping == &inode->i_data but,
+ * this may not be true for device special inodes.
+ */
+ return (struct resv_map *)(&inode->i_data)->private_data;
}

static struct resv_map *vma_resv_map(struct vm_area_struct *vma)
@@ -4477,6 +4485,11 @@ int hugetlb_reserve_pages(struct inode *inode,
* called to make the mapping read-write. Assume !vma is a shm mapping
*/
if (!vma || vma->vm_flags & VM_MAYSHARE) {
+ /*
+ * resv_map can not be NULL as hugetlb_reserve_pages is only
+ * called for inodes for which resv_maps were created (see
+ * hugetlbfs_get_inode).
+ */
resv_map = inode_resv_map(inode);

chg = region_chg(resv_map, from, to);
@@ -4568,6 +4581,10 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
struct hugepage_subpool *spool = subpool_inode(inode);
long gbl_reserve;

+ /*
+ * Since this routine can be called in the evict inode path for all
+ * hugetlbfs inodes, resv_map could be NULL.
+ */
if (resv_map) {
chg = region_del(resv_map, start, end);
/*
--
2.20.1
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