On 2024/9/2 21:01, Julian Sun wrote:
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
Go back to the root cause, I have no idea why it can leave dirty inode
while mkdir races w/ readonly remount, due to the two operations should
be exclusive, IIUC.
- mkdir
- do_mkdirat
- filename_create
- mnt_want_write
- mnt_get_write_access
- mount
- do_remount
- reconfigure_super
- sb_prepare_remount_readonly
- mnt_hold_writers
- vfs_mkdir
- f2fs_mkdir
But when I try to reproduce this bug w/ reproducer provided by syzbot,
I have found a clue in the log:
"skip recovering inline_dots inode..."
So I doubt the root cause is __recover_dot_dentries() in f2fs_lookup()
generates dirty data/meta, in this path, we will not grab related lock
to exclude readonly remount.
Let me try to verify below patch:
https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git/commit/?h=wip&id=69dc8fbbbb39f85f9f436ca562c98afbcc2a48d2
Thanks,
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes:
https://syzkaller.appspot.com/bug?extid=ebea2790904673d7c618
Fixes: ca7d802a7d8e ("f2fs: detect dirty inode in evict_inode")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Julian Sun <sunjunchao2870@xxxxxxxxx>
---
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,
