[PATCH] f2fs: fix to account total free nid correctly

[Chao Yu]

Thread A		Thread B		Thread C
- f2fs_create
 - f2fs_new_inode
  - f2fs_lock_op
   - alloc_nid
    alloc last nid
  - f2fs_unlock_op
			- f2fs_create
			 - f2fs_new_inode
			  - f2fs_lock_op
			   - alloc_nid
			    as node count still not
			    be increased, we will
			    loop in alloc_nid
						- f2fs_write_node_pages
						 - f2fs_balance_fs_bg
						  - f2fs_sync_fs
						   - write_checkpoint
						    - block_operations
						     - f2fs_lock_all
 - f2fs_lock_op

While creating new inode, we do not allocate and account nid atomically,
so that when there is almost no free nids left, we may encounter deadloop
like above stack.

In order to avoid that, add nm_i::free_nid_cnt for accounting free nids
and do nid allocation atomically during node creation.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 fs/f2fs/f2fs.h |  1 +
 fs/f2fs/node.c | 19 +++++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 6de1fbf..9de6f20 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -551,6 +551,7 @@ struct f2fs_nm_info {
 	struct radix_tree_root free_nid_root;/* root of the free_nid cache */
 	struct list_head nid_list[MAX_NID_LIST];/* lists for free nids */
 	unsigned int nid_cnt[MAX_NID_LIST];	/* the number of free node id */
+	unsigned int free_nid_cnt;	/* the number of total free nid */
 	spinlock_t nid_list_lock;	/* protect nid lists ops */
 	struct mutex build_lock;	/* lock for build free nids */
 
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index d58438f..e412d0e 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1885,11 +1885,13 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 		return false;
 	}
 #endif
-	if (unlikely(sbi->total_valid_node_count + 1 > nm_i->available_nids))
-		return false;
-
 	spin_lock(&nm_i->nid_list_lock);
 
+	if (unlikely(nm_i->free_nid_cnt == 0)) {
+		spin_unlock(&nm_i->nid_list_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)) {
 		f2fs_bug_on(sbi, list_empty(&nm_i->nid_list[FREE_NID_LIST]));
@@ -1900,6 +1902,7 @@ bool alloc_nid(struct f2fs_sb_info *sbi, nid_t *nid)
 		__remove_nid_from_list(sbi, i, FREE_NID_LIST, true);
 		i->state = NID_ALLOC;
 		__insert_nid_to_list(sbi, i, ALLOC_NID_LIST, false);
+		nm_i->free_nid_cnt--;
 		spin_unlock(&nm_i->nid_list_lock);
 		return true;
 	}
@@ -1951,6 +1954,9 @@ void alloc_nid_failed(struct f2fs_sb_info *sbi, nid_t nid)
 		i->state = NID_NEW;
 		__insert_nid_to_list(sbi, i, FREE_NID_LIST, false);
 	}
+
+	nm_i->free_nid_cnt++;
+
 	spin_unlock(&nm_i->nid_list_lock);
 
 	if (need_free)
@@ -2222,8 +2228,12 @@ static void __flush_nat_entry_set(struct f2fs_sb_info *sbi,
 		raw_nat_from_node_info(raw_ne, &ne->ni);
 		nat_reset_flag(ne);
 		__clear_nat_cache_dirty(NM_I(sbi), ne);
-		if (nat_get_blkaddr(ne) == NULL_ADDR)
+		if (nat_get_blkaddr(ne) == NULL_ADDR) {
 			add_free_nid(sbi, nid, false);
+			spin_lock(&NM_I(sbi)->nid_list_lock);
+			NM_I(sbi)->free_nid_cnt++;
+			spin_unlock(&NM_I(sbi)->nid_list_lock);
+		}
 	}
 
 	if (to_journal)
@@ -2302,6 +2312,7 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
 	nm_i->nid_cnt[FREE_NID_LIST] = 0;
 	nm_i->nid_cnt[ALLOC_NID_LIST] = 0;
 	nm_i->nat_cnt = 0;
+	nm_i->free_nid_cnt = nm_i->available_nids - sbi->total_valid_node_count;
 	nm_i->ram_thresh = DEF_RAM_THRESHOLD;
 	nm_i->ra_nid_pages = DEF_RA_NID_PAGES;
 	nm_i->dirty_nats_ratio = DEF_DIRTY_NAT_RATIO_THRESHOLD;
-- 
2.8.2.311.gee88674