linux-kernel - Re: NFS/TCP crashes on MIPS/RBTX4927 in v4.20-rcX (bisected)

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Date:   Wed, 5 Dec 2018 13:45:34 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     "geert@...ux-m68k.org" <geert@...ux-m68k.org>,
        "anemo@....ocn.ne.jp" <anemo@....ocn.ne.jp>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: NFS/TCP crashes on MIPS/RBTX4927 in v4.20-rcX (bisected)

On Wed, 2018-12-05 at 14:41 +0100, Geert Uytterhoeven wrote:
> Hi Nemoto-san,
> 
> On Wed, Dec 5, 2018 at 2:11 PM Atsushi Nemoto <anemo@....ocn.ne.jp>
> wrote:
> > On Tue, 4 Dec 2018 14:53:07 +0100, Geert Uytterhoeven <
> > geert@...ux-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

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com