linux-kernel - Re: [syzbot] [hfs?] WARNING in hfs_write

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Message-ID: <23b19f18-13a3-1744-cdce-801cfa35a807@linux-m68k.org>
Date:   Fri, 21 Jul 2023 11:45:39 +1000 (AEST)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Dave Chinner <david@...morbit.com>,
        Jeff Layton <jlayton@...nel.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Viacheslav Dubeyko <slava@...eyko.com>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        syzbot <syzbot+7bb7cd3595533513a9e7@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        christian.brauner@...ntu.com,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com,
        ZhangPeng <zhangpeng362@...wei.com>,
        linux-m68k@...ts.linux-m68k.org,
        debian-ports <debian-ports@...ts.debian.org>
Subject: Re: [syzbot] [hfs?] WARNING in hfs_write_inode

On Fri, 21 Jul 2023, Matthew Wilcox wrote:

> On Fri, Jul 21, 2023 at 11:03:28AM +1000, Finn Thain wrote:
> > On Fri, 21 Jul 2023, Dave Chinner wrote:
> > 
> > > > I suspect that this is one of those catch-22 situations: distros 
> > > > are going to enable every feature under the sun. That doesn't mean 
> > > > that anyone is actually _using_ them these days.
> > 
> > I think the value of filesystem code is not just a question of how 
> > often it gets executed -- it's also about retaining access to the data 
> > collected in archives, museums, galleries etc. that is inevitably held 
> > in old formats.
> 
> That's an argument for adding support to tar, not for maintaining 
> read/write support.
> 

I rather think it's an argument for collaboration between the interested 
parties upstream (inluding tar developers). As I see it, the question is, 
what kind of "upstream" is best for that?

> > > We need to much more proactive about dropping support for 
> > > unmaintained filesystems that nobody is ever fixing despite the 
> > > constant stream of corruption- and deadlock- related bugs reported 
> > > against them.
> > 
> > IMO, a stream of bug reports is not a reason to remove code (it's a 
> > reason to revert some commits).
> > 
> > Anyway, that stream of bugs presumably flows from the unstable kernel 
> > API, which is inherently high-maintenance. It seems that a stable API 
> > could be more appropriate for any filesystem for which the on-disk 
> > format is fixed (by old media, by unmaintained FLOSS implementations 
> > or abandoned proprietary implementations).
> 
> You've misunderstood.  Google have decided to subject the entire kernel 
> (including obsolete unmaintained filesystems) to stress tests that it's 
> never had before.  IOW these bugs have been there since the code was 
> merged.  There's nothing to back out.  There's no API change to blame. 
> It's always been buggy and it's never mattered before.
> 

I see. Thanks for providing that background.

> It wouldn't be so bad if Google had also decided to fund people to fix 
> those bugs, but no, they've decided to dump them on public mailing lists 
> and berate developers into fixing them.
> 

Those bugs, if moved from kernel to userspace, would be less harmful, 
right?