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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 5 Dec 2018 15:47:45 +0100
Message-ID: <CAMuHMdXyfEVOWoBOx0Ywm6vw5oQ6eHNXFhQBKTfRSBOmPYGM6Q@mail.gmail.com>
Subject: Re: NFS/TCP crashes on MIPS/RBTX4927 in v4.20-rcX (bisected)
To:     trondmy@hammerspace.com
Cc:     Atsushi Nemoto <anemo@mba.ocn.ne.jp>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>,
        linux-mips@vger.kernel.org
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Hi Trond,

On Wed, Dec 5, 2018 at 2:45 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
> On Wed, 2018-12-05 at 14:41 +0100, Geert Uytterhoeven wrote:
> > On Wed, Dec 5, 2018 at 2:11 PM Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> > wrote:
> > > On Tue, 4 Dec 2018 14:53:07 +0100, Geert Uytterhoeven <
> > > geert@linux-m68k.org> wrote:
> > > > I found similar crashes in a report from 2006, but of course the
> > > > code
> > > > has changed too much to apply the solution proposed there
> > > > (
> > > > https://www.linux-mips.org/archives/linux-mips/2006-09/msg00169.html
> > > > ).
> > > >
> > > > Userland is Debian 8 (the last release supporting "old" MIPS).
> > > > My kernel is based on v4.20.0-rc5, but the issue happens with
> > > > v4.20-rc1,
> > > > too.
> > > >
> > > > However, I noticed it works in v4.19! Hence I've bisected this,
> > > > to commit
> > > > 277e4ab7d530bf28 ("SUNRPC: Simplify TCP receive code by switching
> > > > to using
> > > > iterators").
> > > >
> > > > Dropping the ",tcp" part from the nfsroot parameter also fixes
> > > > the issue.
> > > >
> > > > Given RBTX4927 is little endian, just like my arm/arm64 boards,
> > > > it's probably
> > > > not an endianness issue.  Sparse didn't show anything suspicious
> > > > before/after
> > > > the guilty commit.
> > > >
> > > > Do you have a clue?
> > >
> > > If it was a cache issue, disabling i-cache or d-cache completely
> > > might
> > > help understanding the problem.  I added TXx9 specific "icdisable"
> > > and
> > > "dcdisable" kernel options for debugging long ago.
> > >
> > > I hope these options still works correctly with recent kernel but
> > > not
> > > sure.
> > >
> > > Also, disabling i-cache makes your board VERY slow, of course.
> >
> > Thanks!
> >
> > When using these options, I do see a slowdown in early boot, but the
> > issue
> > is still there.
> >
> > My next guess is an unaligned access not using {get,put}_unaligned(),
> > which
> > doesn't seem to work on tx4927, but doesn't cause an exception
> > neither.
>
> Can you try my linux-next branch on git.linux-nfs.org? It contains a
> fixes for a hang that results from the above commit.
>
> git pull git://git.linux-nfs.org/projects/trondmy/linux-nfs.git linux-next

Thanks for the suggestion, but unfortunately it doesn't help.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds