linux-kernel - Re: WARNING: filesystem loop0 was created with 512 inodes, the real maximum is 511, mounting anyway

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Date:   Mon, 7 Dec 2020 14:13:27 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tigran Aivazian <aivazian.tigran@...il.com>
Cc:     syzbot <syzbot+54b10a5da9e59f1ed979@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING: filesystem loop0 was created with 512 inodes, the real
 maximum is 511, mounting anyway

On Mon, Sep 28, 2020 at 11:08 AM Tigran Aivazian
<aivazian.tigran@...il.com> wrote:
>
> On Mon, 28 Sep 2020 at 09:29, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > On Mon, Sep 28, 2020 at 10:23 AM Tigran Aivazian
> > > No, this is not an issue. In the latest change to BFS I added the
> > > following comment to the header fs/bfs/bfs.h, which explains it:
> > >
> > > /* In theory BFS supports up to 512 inodes, numbered from 2 (for /) up
> > > to 513 inclusive.
> > >    In actual fact, attempting to create the 512th inode (i.e. inode
> > > No. 513 or file No. 511)
> > >    will fail with ENOSPC in bfs_add_entry(): the root directory cannot
> > > contain so many entries, counting '..'.
> > >    So, mkfs.bfs(8) should really limit its -N option to 511 and not
> > > 512. For now, we just print a warning
> > >    if a filesystem is mounted with such "impossible to fill up" number
> > > of inodes */
> >
> > There are rules for use of "WARNING" in output required to support
> > kernel testing:
> > https://github.com/torvalds/linux/blob/master/include/asm-generic/bug.h#L67-L80
> > This seems to be triggerable by exteranal inputs and breaks these rules.
>
> Thank you, I didn't know about these rules. Ok, then, since this
> warning does not "need prompt attention if it should ever occur at
> runtime", the easiest solution is to change "WARNING" to lower case
> "warning" in that printk in fs/bfs/inode.c:
>
> --- fs/bfs/inode.c.0 2020-09-28 10:03:00.658549556 +0100
> +++ fs/bfs/inode.c 2020-09-28 10:03:05.408548250 +0100
> @@ -351,7 +351,7 @@
>
>   info->si_lasti = (le32_to_cpu(bfs_sb->s_start) - BFS_BSIZE) /
> sizeof(struct bfs_inode) + BFS_ROOT_INO - 1;
>   if (info->si_lasti == BFS_MAX_LASTI)
> - printf("WARNING: filesystem %s was created with 512 inodes, the real
> maximum is 511, mounting anyway\n", s->s_id);
> + printf("warning: filesystem %s was created with 512 inodes, the real
> maximum is 511, mounting anyway\n", s->s_id);
>   else if (info->si_lasti > BFS_MAX_LASTI) {
>   printf("Impossible last inode number %lu > %d on %s\n",
> info->si_lasti, BFS_MAX_LASTI, s->s_id);
>   goto out1;
>
> If you want to submit this patch to the appropriate place(s), feel
> free to do this -- I approve it. If the comment in asm/bug.h is
> inaccurate and its mention of "BUG/WARNING" implies the lowercase
> "bug/warning" also, then one can remove the prefix "warning: " from
> the patch altogether and proper case "filesystem" to "Filesystem".
>
> Kind regards,
> Tigran
>
> Acked-By: Tigran Aivazian <aivazian.tigran@...il.com>
> Approved-By: Tigran Aivazian <aivazian.tigran@...il.com>


#syz fix: bfs: don't use WARNING: string when it's just info.