Re: [f2fs-dev] [PATCH] f2fs: fix missing mapping caused by the mount/umount race

From: Chao Yu
Date: Thu Sep 08 2022 - 06:54:58 EST

On 2022/8/31 11:05, Jaegeuk Kim wrote:
On 08/30, Jaegeuk Kim wrote:
On 08/30, Chao Yu wrote:
On 2022/8/30 5:52, Jaegeuk Kim wrote:
Sometimes we can get a cached meta_inode which has no aops yet. Let's set it
all the time to fix the below panic.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:
ESR = 0x0000000086000004
EC = 0x21: IABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
user pgtable: 4k pages, 48-bit VAs, pgdp=0000000109ee4000
[0000000000000000] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 86000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 3045 Comm: syz-executor330 Not tainted 6.0.0-rc2-syzkaller-16455-ga41a877bc12d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : 0x0
lr : folio_mark_dirty+0xbc/0x208 mm/page-writeback.c:2748
sp : ffff800012783970
x29: ffff800012783970 x28: 0000000000000000 x27: ffff800012783b08
x26: 0000000000000001 x25: 0000000000000400 x24: 0000000000000001
x23: ffff0000c736e000 x22: 0000000000000045 x21: 05ffc00000000015
x20: ffff0000ca7403b8 x19: fffffc00032ec600 x18: 0000000000000181
x17: ffff80000c04d6bc x16: ffff80000dbb8658 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: ff808000083e9814 x10: 0000000000000000 x9 : ffff8000083e9814
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
x5 : ffff0000cbb19000 x4 : ffff0000cb3d2000 x3 : ffff0000cbb18f80
x2 : fffffffffffffff0 x1 : fffffc00032ec600 x0 : ffff0000ca7403b8
Call trace:
set_page_dirty+0x38/0xbc mm/folio-compat.c:62
f2fs_update_meta_page+0x80/0xa8 fs/f2fs/segment.c:2369
do_checkpoint+0x794/0xea8 fs/f2fs/checkpoint.c:1522
f2fs_write_checkpoint+0x3b8/0x568 fs/f2fs/checkpoint.c:1679

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+775a3440817f74fddb8c@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
fs/f2fs/inode.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 6d11c365d7b4..1feb0a8a699e 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -490,10 +490,7 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
if (!inode)
return ERR_PTR(-ENOMEM);
- if (!(inode->i_state & I_NEW)) {
- trace_f2fs_iget(inode);
- return inode;
- }
+ /* We can see an old cached inode. Let's set the aops all the time. */

Why an old cached inode (has no I_NEW flag) has NULL a_ops pointer? If it is a bad
inode, it should be unhashed before unlock_new_inode().

I'm trying to dig further tho, it's not a bad inode, nor I_FREEING | I_CLEAR.
It's very werid that thie meta inode is found in newly created superblock by
the global hash table. I've checked that the same superblock pointer was used
in the previous tests, but inode was evictied all the time.

I'll drop this patch, since it turned out there is a bug in reiserfs which
doesn't free the root inode (ino=2). That leads f2fs to find an ino=2 with
the previous superblock point used by reiserfs. That stale inode has no valid
inode that f2fs can use. I tried to find where the root cause is in reiserfs,
but it seems quite hard to catch one.

- reiserfs_fill_super
- reiserfs_xattr_init
- create_privroot
- xattr_mkdir
- reiserfs_new_inode
- reiserfs_get_unused_objectid returned 0 due to map crash

It seems the error path doesn't handle the root inode properly.

Nice catch!

Could you please check:

f2fs: fix to detect obsolete inner inode during fill_super()



if (ino == F2FS_NODE_INO(sbi) || ino == F2FS_META_INO(sbi))
goto make_now;
@@ -502,6 +499,11 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
goto make_now;
+ if (!(inode->i_state & I_NEW)) {
+ trace_f2fs_iget(inode);
+ return inode;
+ }
ret = do_read_inode(inode);
if (ret)
goto bad_inode;
@@ -557,7 +559,8 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
- unlock_new_inode(inode);
+ if (inode->i_state & I_NEW)
+ unlock_new_inode(inode);
return inode;

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