f2fs: fix to avoid f2fs_bug_on() in dec_valid_node_count()

As Yanming reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=215897

I have encountered a bug in F2FS file system in kernel v5.17.

The kernel should enable CONFIG_KASAN=y and CONFIG_KASAN_INLINE=y. You can
reproduce the bug by running the following commands:

The kernel message is shown below:

kernel BUG at fs/f2fs/f2fs.h:2511!
Call Trace:
 f2fs_remove_inode_page+0x2a2/0x830
 f2fs_evict_inode+0x9b7/0x1510
 evict+0x282/0x4e0
 do_unlinkat+0x33a/0x540
 __x64_sys_unlinkat+0x8e/0xd0
 do_syscall_64+0x3b/0x90
 entry_SYSCALL_64_after_hwframe+0x44/0xae

The root cause is: .total_valid_block_count or .total_valid_node_count
could fuzzed to zero, then once dec_valid_node_count() was called, it
will cause BUG_ON(), this patch fixes to print warning info and set
SBI_NEED_FSCK into CP instead of panic.

Cc: stable@vger.kernel.org
Reported-by: Ming Yan <yanming@tju.edu.cn>
Signed-off-by: Chao Yu <chao.yu@oppo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/f2fs.h

@@ -2605,11 +2605,17 @@ static inline void dec_valid_node_count(struct f2fs_sb_info *sbi,
 {
 	spin_lock(&sbi->stat_lock);
 
-	f2fs_bug_on(sbi, !sbi->total_valid_block_count);
-	f2fs_bug_on(sbi, !sbi->total_valid_node_count);
+	if (unlikely(!sbi->total_valid_block_count ||
+			!sbi->total_valid_node_count)) {
+		f2fs_warn(sbi, "dec_valid_node_count: inconsistent block counts, total_valid_block:%u, total_valid_node:%u",
+			  sbi->total_valid_block_count,
+			  sbi->total_valid_node_count);
+		set_sbi_flag(sbi, SBI_NEED_FSCK);
+	} else {
+		sbi->total_valid_block_count--;
+		sbi->total_valid_node_count--;
+	}
 
-	sbi->total_valid_node_count--;
-	sbi->total_valid_block_count--;
 	if (sbi->reserved_blocks &&
 		sbi->current_reserved_blocks < sbi->reserved_blocks)
 		sbi->current_reserved_blocks++;