[PATCH] f2fs: Do not check the FI_DIRTY_INODE flag when umounting a ro fs.

[Julian Sun <sunjunchao2870@gmail.com>]

Hi, all.

Recently syzbot reported a bug as following:

kernel BUG at fs/f2fs/inode.c:896!
CPU: 1 UID: 0 PID: 5217 Comm: syz-executor605 Not tainted 6.11.0-rc4-syzkaller-00033-g872cf28b8df9 #0
RIP: 0010:f2fs_evict_inode+0x1598/0x15c0 fs/f2fs/inode.c:896
Call Trace:
 <TASK>
 evict+0x532/0x950 fs/inode.c:704
 dispose_list fs/inode.c:747 [inline]
 evict_inodes+0x5f9/0x690 fs/inode.c:797
 generic_shutdown_super+0x9d/0x2d0 fs/super.c:627
 kill_block_super+0x44/0x90 fs/super.c:1696
 kill_f2fs_super+0x344/0x690 fs/f2fs/super.c:4898
 deactivate_locked_super+0xc4/0x130 fs/super.c:473
 cleanup_mnt+0x41f/0x4b0 fs/namespace.c:1373
 task_work_run+0x24f/0x310 kernel/task_work.c:228
 ptrace_notify+0x2d2/0x380 kernel/signal.c:2402
 ptrace_report_syscall include/linux/ptrace.h:415 [inline]
 ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
 syscall_exit_work+0xc6/0x190 kernel/entry/common.c:173
 syscall_exit_to_user_mode_prepare kernel/entry/common.c:200 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:205 [inline]
 syscall_exit_to_user_mode+0x279/0x370 kernel/entry/common.c:218
 do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The syzbot constructed the following scenario: concurrently
creating directories and setting the file system to read-only.
In this case, while f2fs was making dir, the filesystem switched to
readonly, and when it tried to clear the dirty flag, it triggered this
code path: f2fs_mkdir()-> f2fs_sync_fs()->f2fs_write_checkpoint()
->f2fs_readonly(). This resulted FI_DIRTY_INODE flag not being cleared,
which eventually led to a bug being triggered during the FI_DIRTY_INODE
check in f2fs_evict_inode().

In this case, we cannot do anything further, so if filesystem is readonly,
do not trigger the BUG. Instead, clean up resources to the best of our
ability to prevent triggering subsequent resource leak checks.

If there is anything important I'm missing, please let me know, thanks.

Reported-by: syzbot+ebea2790904673d7c618@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ebea2790904673d7c618
Fixes: ca7d802a7d8e ("f2fs: detect dirty inode in evict_inode")
CC: stable@vger.kernel.org
Signed-off-by: Julian Sun <sunjunchao2870@gmail.com>
---
 fs/f2fs/inode.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index aef57172014f..52d273383ec2 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -892,8 +892,12 @@ void f2fs_evict_inode(struct inode *inode)
 			atomic_read(&fi->i_compr_blocks));
 
 	if (likely(!f2fs_cp_error(sbi) &&
-				!is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
-		f2fs_bug_on(sbi, is_inode_flag_set(inode, FI_DIRTY_INODE));
+				!is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
+		if (!f2fs_readonly(sbi->sb))
+			f2fs_bug_on(sbi, is_inode_flag_set(inode, FI_DIRTY_INODE));
+		else
+			f2fs_inode_synced(inode);
+	}
 	else
 		f2fs_inode_synced(inode);
 
-- 
2.39.2