[PATCH v2] f2fs: fix race condition in between free nid allocator/initializer

[Chao Yu]

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 uses build_lock covering free nid allocation and initialization
to avoid this race condition.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
v2: fix deadlock in remove_free_nid.
 fs/f2fs/node.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 4f89478be683..d12b00dc9d26 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -22,8 +22,6 @@
 #include "trace.h"
 #include <trace/events/f2fs.h>
 
-#define on_build_free_nids(nmi) mutex_is_locked(&nm_i->build_lock)
-
 static struct kmem_cache *nat_entry_slab;
 static struct kmem_cache *free_nid_slab;
 static struct kmem_cache *nat_entry_set_slab;
@@ -2000,15 +1998,18 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 		return false;
 	}
 #endif
+
+	mutex_lock(&nm_i->build_lock);
 	spin_lock(&nm_i->nid_list_lock);
 
 	if (unlikely(nm_i->available_nids == 0)) {
 		spin_unlock(&nm_i->nid_list_lock);
+		mutex_unlock(&nm_i->build_lock);
 		return false;
 	}
 
 	/* We should not use stale free nids created by build_free_nids */
-	if (nm_i->nid_cnt[FREE_NID_LIST] && !on_build_free_nids(nm_i)) {
+	if (nm_i->nid_cnt[FREE_NID_LIST]) {
 		f2fs_bug_on(sbi, list_empty(&nm_i->nid_list[FREE_NID_LIST]));
 		i = list_first_entry(&nm_i->nid_list[FREE_NID_LIST],
 					struct free_nid, list);
@@ -2022,9 +2023,11 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 		update_free_nid_bitmap(sbi, *nid, false, false);
 
 		spin_unlock(&nm_i->nid_list_lock);
+		mutex_unlock(&nm_i->build_lock);
 		return true;
 	}
 	spin_unlock(&nm_i->nid_list_lock);
+	mutex_unlock(&nm_i->build_lock);
 
 	/* Let's scan nat pages and its caches to get free nids */
 	build_free_nids(sbi, true, false);
@@ -2039,11 +2042,13 @@ void alloc_nid_done(struct f2fs_sb_info *sbi, nid_t nid)
 	struct f2fs_nm_info *nm_i = NM_I(sbi);
 	struct free_nid *i;
 
+	mutex_lock(&nm_i->build_lock);
 	spin_lock(&nm_i->nid_list_lock);
 	i = __lookup_free_nid_list(nm_i, nid);
 	f2fs_bug_on(sbi, !i);
 	__remove_nid_from_list(sbi, i, ALLOC_NID_LIST, false);
 	spin_unlock(&nm_i->nid_list_lock);
+	mutex_unlock(&nm_i->build_lock);
 
 	kmem_cache_free(free_nid_slab, i);
 }
@@ -2060,6 +2065,7 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
 	if (!nid)
 		return;
 
+	mutex_lock(&nm_i->build_lock);
 	spin_lock(&nm_i->nid_list_lock);
 	i = __lookup_free_nid_list(nm_i, nid);
 	f2fs_bug_on(sbi, !i);
@@ -2078,6 +2084,7 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
 	update_free_nid_bitmap(sbi, nid, true, false);
 
 	spin_unlock(&nm_i->nid_list_lock);
+	mutex_unlock(&nm_i->build_lock);
 
 	if (need_free)
 		kmem_cache_free(free_nid_slab, i);
@@ -2445,6 +2452,7 @@ void flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	if (!nm_i->dirty_nat_cnt)
 		return;
 
+	mutex_lock(&nm_i->build_lock);
 	down_write(&nm_i->nat_tree_lock);
 
 	/*
@@ -2470,6 +2478,8 @@ void flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 		__flush_nat_entry_set(sbi, set, cpc);
 
 	up_write(&nm_i->nat_tree_lock);
+	mutex_unlock(&nm_i->build_lock);
+
 	/* Allow dirty nats by node block allocation in write_begin */
 }
 
-- 
2.8.2.295.g3f1c1d0