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Subject[PATCH 4.9 084/101] f2fs: fix race condition in between free nid allocator/initializer
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chao Yu <yuchao0@huawei.com>

commit 30a61ddf8117c26ac5b295e1233eaa9629a94ca3 upstream.

In below concurrent case, allocated nid can be loaded into free nid cache
and be allocated again.

Thread A Thread B
- f2fs_create
- f2fs_new_inode
- alloc_nid
- __insert_nid_to_list(ALLOC_NID_LIST)
- f2fs_balance_fs_bg
- build_free_nids
- __build_free_nids
- scan_nat_page
- add_free_nid
- __lookup_nat_cache
- f2fs_add_link
- init_inode_metadata
- new_inode_page
- new_node_page
- set_node_addr
- alloc_nid_done
- __remove_nid_from_list(ALLOC_NID_LIST)
- __insert_nid_to_list(FREE_NID_LIST)

This patch makes nat cache lookup and free nid list operation being atomical
to avoid this race condition.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
[bwh: Backported to 4.9:
- add_free_nid() returns 0 in case of any error (except low memory)
- Tree/list addition has not been moved into __insert_nid_to_list()]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/f2fs/node.c | 62 +++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 43 insertions(+), 19 deletions(-)

--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1704,8 +1704,9 @@ static void __del_from_free_nid_list(str
static int add_free_nid(struct f2fs_sb_info *sbi, nid_t nid, bool build)
{
struct f2fs_nm_info *nm_i = NM_I(sbi);
- struct free_nid *i;
+ struct free_nid *i, *e;
struct nat_entry *ne;
+ int err = -EINVAL;

if (!available_free_memory(sbi, FREE_NIDS))
return -1;
@@ -1714,35 +1715,58 @@ static int add_free_nid(struct f2fs_sb_i
if (unlikely(nid == 0))
return 0;

- if (build) {
- /* do not add allocated nids */
- ne = __lookup_nat_cache(nm_i, nid);
- if (ne && (!get_nat_flag(ne, IS_CHECKPOINTED) ||
- nat_get_blkaddr(ne) != NULL_ADDR))
- return 0;
- }
-
i = f2fs_kmem_cache_alloc(free_nid_slab, GFP_NOFS);
i->nid = nid;
i->state = NID_NEW;

- if (radix_tree_preload(GFP_NOFS)) {
- kmem_cache_free(free_nid_slab, i);
- return 0;
- }
+ if (radix_tree_preload(GFP_NOFS))
+ goto err;

spin_lock(&nm_i->free_nid_list_lock);
- if (radix_tree_insert(&nm_i->free_nid_root, i->nid, i)) {
- spin_unlock(&nm_i->free_nid_list_lock);
- radix_tree_preload_end();
- kmem_cache_free(free_nid_slab, i);
- return 0;
+
+ if (build) {
+ /*
+ * Thread A Thread B
+ * - f2fs_create
+ * - f2fs_new_inode
+ * - alloc_nid
+ * - __insert_nid_to_list(ALLOC_NID_LIST)
+ * - f2fs_balance_fs_bg
+ * - build_free_nids
+ * - __build_free_nids
+ * - scan_nat_page
+ * - add_free_nid
+ * - __lookup_nat_cache
+ * - f2fs_add_link
+ * - init_inode_metadata
+ * - new_inode_page
+ * - new_node_page
+ * - set_node_addr
+ * - alloc_nid_done
+ * - __remove_nid_from_list(ALLOC_NID_LIST)
+ * - __insert_nid_to_list(FREE_NID_LIST)
+ */
+ ne = __lookup_nat_cache(nm_i, nid);
+ if (ne && (!get_nat_flag(ne, IS_CHECKPOINTED) ||
+ nat_get_blkaddr(ne) != NULL_ADDR))
+ goto err_out;
+
+ e = __lookup_free_nid_list(nm_i, nid);
+ if (e)
+ goto err_out;
}
+ if (radix_tree_insert(&nm_i->free_nid_root, i->nid, i))
+ goto err_out;
+ err = 0;
list_add_tail(&i->list, &nm_i->free_nid_list);
nm_i->fcnt++;
+err_out:
spin_unlock(&nm_i->free_nid_list_lock);
radix_tree_preload_end();
- return 1;
+err:
+ if (err)
+ kmem_cache_free(free_nid_slab, i);
+ return !err;
}

static void remove_free_nid(struct f2fs_nm_info *nm_i, nid_t nid)

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