RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"

David Laight
2020-11-02T18:23:16Z

From: 'Greg KH'
> Sent: 02 November 2020 13:52
>
> On Mon, Nov 02, 2020 at 09:06:38AM +0000, David Laight wrote:
> > From: 'Greg KH'
> > > Sent: 23 October 2020 15:47
> > >
> > > On Fri, Oct 23, 2020 at 02:39:24PM +0000, David Laight wrote:
> > > > From: David Hildenbrand
> > > > > Sent: 23 October 2020 15:33
> > > > ...
> > > > > I just checked against upstream code generated by clang 10 and it
> > > > > properly discards the upper 32bit via a mov w23 w2.
> > > > >
> > > > > So at least clang 10 indeed properly assumes we could have garbage and
> > > > > masks it off.
> > > > >
> > > > > Maybe the issue is somewhere else, unrelated to nr_pages ... or clang 11
> > > > > behaves differently.
> > > >
> > > > We'll need the disassembly from a failing kernel image.
> > > > It isn't that big to hand annotate.
> > >
> > > I've worked around the merge at the moment in the android tree, but it
> > > is still quite reproducable, and will try to get a .o file to
> > > disassemble on Monday or so...
> >
> > Did this get properly resolved?
>
> For some reason, 5.10-rc2 fixed all of this up. I backed out all of the
> patches I had to revert to get 5.10-rc1 to work properly, and then did
> the merge and all is well.
>
> It must have been something to do with the compat changes in this same
> area that went in after 5.10-rc1, and something got reorganized in the
> files somehow. I really do not know, and at the moment, don't have the
> time to track it down anymore. So for now, I'd say it's all good, sorry
> for the noise.

Hopefully it won't appear again.

Saved me spending a day off reading arm64 assembler.

David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)