linux-kernel - Re: [PATCH v2] hfs: remove BUG() from hfs_release_folio()/hfs_test_inode()/hfs_write

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Message-ID: <4c1eb34018cabe33f81b1aa13d5eb0adc44661e7.camel@dubeyko.com>
Date: Tue, 15 Jul 2025 12:20:17 -0700
From: Viacheslav Dubeyko <slava@...eyko.com>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>, John Paul Adrian
 Glaubitz <glaubitz@...sik.fu-berlin.de>, Yangtao Li <frank.li@...o.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-fsdevel
	 <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
 Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2] hfs: remove BUG() from
 hfs_release_folio()/hfs_test_inode()/hfs_write_inode()

On Tue, 2025-07-15 at 15:51 +0900, Tetsuo Handa wrote:
> Since syzkaller can mount crafted filesystem images with inode->ino
> == 0
> (which is not listed as "Some special File ID numbers" in
> fs/hfs/hfs.h ),
> replace BUG() with pr_warn().
> 
> Reported-by: syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b
> Tested-by: syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  fs/hfs/inode.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
> index a81ce7a740b9..794d710c3ae0 100644
> --- a/fs/hfs/inode.c
> +++ b/fs/hfs/inode.c
> @@ -81,7 +81,7 @@ static bool hfs_release_folio(struct folio *folio,
> gfp_t mask)
>  		tree = HFS_SB(sb)->cat_tree;
>  		break;
>  	default:
> -		BUG();
> +		pr_warn("unexpected inode %lu at %s()\n", inode-
> >i_ino, __func__);

I don't think that it makes sense to add the function name here. I
understand that you would like to be informative here. But, usually,
HFS code doesn't show the the function name in error messages.

By the way, why are you using pr_warn() but not pr_err()? Any
particular reason to use namely pr_warn()?

We had BUG() here before and, potentially, we could use pr_warn() +
dump_stack() to be really informative here.

>  		return false;
>  	}
>  
> @@ -305,7 +305,7 @@ static int hfs_test_inode(struct inode *inode,
> void *data)
>  	case HFS_CDR_FIL:
>  		return inode->i_ino == be32_to_cpu(rec->file.FlNum);
>  	default:
> -		BUG();
> +		pr_warn("unexpected type %u at %s()\n", rec->type,
> __func__);

Ditto.

>  		return 1;
>  	}
>  }
> @@ -441,7 +441,7 @@ int hfs_write_inode(struct inode *inode, struct
> writeback_control *wbc)
>  			hfs_btree_write(HFS_SB(inode->i_sb)-
> >cat_tree);
>  			return 0;
>  		default:
> -			BUG();
> +			pr_warn("unexpected inode %lu at %s()\n",
> inode->i_ino, __func__);

Ditto.

Thanks,
Slava.

>  			return -EIO;
>  		}
>  	}