linux-kernel - Re: [syzbot] WARNING in iomap

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Message-ID: <182c028abf0.2dc6f7c973088.2963173753499991828@siddh.me>
Date:   Sun, 21 Aug 2022 16:57:47 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     "hch" <hch@...radead.org>
Cc:     "matthew wilcox" <willy@...radead.org>,
        "david" <david@...morbit.com>, "djwong" <djwong@...nel.org>,
        "fgheet255t" <fgheet255t@...il.com>,
        "linux-ext4" <linux-ext4@...r.kernel.org>,
        "linux-fsdevel" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "linux-xfs" <linux-xfs@...r.kernel.org>,
        "riteshh" <riteshh@...ux.ibm.com>,
        "syzbot+a8e049cd3abd342936b6" 
        <syzbot+a8e049cd3abd342936b6@...kaller.appspotmail.com>,
        "syzkaller-bugs" <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] WARNING in iomap_iter

On Sun, 21 Aug 2022 11:59:05 +0530  Christoph Hellwig  wrote:
> On Thu, Aug 18, 2022 at 08:51:16PM +0530, Siddh Raman Pant wrote:
> > On Thu, 18 Aug 2022 20:20:02 +0530  Matthew Wilcox  wrote:
> > > I don't think changing these from u64 to s64 is the right way to go.
> > 
> > Why do you think so? Is there somnething I overlooked?
> > 
> > I think it won't intorduce regression, since if something is working,
> > it will continue to work. If something does break, then they were
> > relying on overflows, which is anyways an incorrect way to go about.
> 
> Well, for example userspace code expecting unsignedness of these
> types could break.  So if we really think changing the types is so
> much preferred we'd need to audit common userspace first.  Because
> of that I think the version proposed by willy is generally preferred.

Alright.

> > Also, it seems even the 32-bit compatibility structure uses signed
> > types.
> 
> We should probably fix that as well.

Isn't having signed type how it is should be though? Or do you mean need
to fix assignment in the conversions (like in loop_info64_from_compat)?

Thanks,
Siddh