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

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Date:   Tue, 30 Aug 2022 11:46:45 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Cc:     syzbot+775a3440817f74fddb8c@...kaller.appspotmail.com,
        stable@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix missing mapping caused by the
 mount/umount race

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:
>   0x0
>   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@...r.kernel.org
> Reported-by: syzbot+775a3440817f74fddb8c@...kaller.appspotmail.com
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>   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().

Thanks,

>   	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;
>   #endif
>   
> +	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)
>   		file_dont_truncate(inode);
>   	}
>   
> -	unlock_new_inode(inode);
> +	if (inode->i_state & I_NEW)
> +		unlock_new_inode(inode);
>   	trace_f2fs_iget(inode);
>   	return inode;
>