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f2fs: fix race condition in between free nid allocator/initializer

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>
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chaseyu authored and Jaegeuk Kim committed Mar 22, 2017
1 parent 5f4c3de commit 30a61ddf8117c26ac5b295e1233eaa9629a94ca3
Showing with 45 additions and 18 deletions.
  1. +45 −18 fs/f2fs/node.c
@@ -1761,40 +1761,67 @@ static void __remove_nid_from_list(struct f2fs_sb_info *sbi,
static bool 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;
int err = -EINVAL;
bool ret = false;

/* 0 nid should not be used */
if (unlikely(nid == 0))
return false;

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 false;
}

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 true;
}
if (radix_tree_preload(GFP_NOFS))
goto err;

spin_lock(&nm_i->nid_list_lock);

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) {
if (e->state == NID_NEW)
ret = true;
goto err_out;
}
}
ret = true;
err = __insert_nid_to_list(sbi, i, FREE_NID_LIST, true);
err_out:
spin_unlock(&nm_i->nid_list_lock);
radix_tree_preload_end();
if (err) {
err:
if (err)
kmem_cache_free(free_nid_slab, i);
return true;
}
return true;
return ret;
}

static void remove_free_nid(struct f2fs_sb_info *sbi, nid_t nid)

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