On Mon, 2024-09-02 at 16:13 +0800, Chao Yu wrote:
On 2024/8/29 0:54, Julian Sun wrote:
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 | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c index aef57172014f..ebf825dba0a5 100644 --- a/fs/f2fs/inode.c +++ b/fs/f2fs/inode.c @@ -892,7 +892,8 @@ 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))) + !is_sbi_flag_set(sbi, SBI_CP_DISABLED)) && + !f2fs_readonly(sbi->sb))
Is it fine to drop this dirty inode? Since once it remounts f2fs as rw one, previous updates on such inode may be lost? Or am I missing something?
The purpose of calling this here is mainly to avoid triggering the f2fs_bug_on(sbi, 1); statement in the subsequent f2fs_put_super() due to a reference count check failure. I would say it's possible, but there doesn't seem to be much more we can do in this scenario: the inode is about to be freed, and the file system is read-only. Or do we need a mechanism to save the inode that is about to be freed and then write it back to disk at the appropriate time after the file system becomes rw again? But such a mechanism sounds somewhat complex and a little bit of weird... Do you have any suggestions?
Thanks,
f2fs_bug_on(sbi, is_inode_flag_set(inode, FI_DIRTY_INODE)); else f2fs_inode_synced(inode);
Thanks,