Re: [PATCH] iomap: handle iterator position advancing beyond current mapping

[Brian Foster <bfoster@redhat.com>]

On Mon, Feb 02, 2026 at 08:05:48AM -0800, Christoph Hellwig wrote:
> On Mon, Feb 02, 2026 at 03:35:39PM +0000, Matthew Wilcox wrote:
> > On Mon, Feb 02, 2026 at 06:48:50AM -0800, Christoph Hellwig wrote:
> > > On Mon, Feb 02, 2026 at 06:30:44PM +0530, Piyush Patle wrote:
> > > > Closes: https://syzkaller.appspot.com/bug?id=bd5ca596a01d01bfa083
> > > 
> > > This link doesn't work.  And the commit log has zero details of what's
> > > happening either.
> > 
> > Looks like this one:
> > 
> > https://syzkaller.appspot.com/bug?extid=bd5ca596a01d01bfa083
> > 
> > but there's no reproducer.  Looks like it's through the blockdev rather
> > than a filesystem being involved.
> 
> Let's wait for a reproducer.  The fix looks incorrect for anything I
> could think of, so I'd rather fix a real bug.  Given that lack of
> reproducer I'm also not confident that it fixes anything.  The fact
> that the Fixes tag points to a merge commit doesn't really increase
> the trust I have in it either.
> 
> 

+1 to this, FWIW. I've had that syzbot report marked in my inbox
expecting (hoping..) it would eventually spit out a reproducer to help
better characterize the cause.

This patch just appears to copy the warning check and force a lookup
cycle before we trigger it, which I don't think is doing us any favors.
At minimum we should have an understanding of precisely how this
happens.

Brian