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Date:   Wed, 05 Dec 2018 22:11:46 +0900 (JST)
Message-Id: <20181205.221146.969453990167463340.anemo@mba.ocn.ne.jp>
To:     geert@linux-m68k.org
Cc:     trond.myklebust@hammerspace.com, linux-nfs@vger.kernel.org,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: NFS/TCP crashes on MIPS/RBTX4927 in v4.20-rcX (bisected)
From:   Atsushi Nemoto <anemo@mba.ocn.ne.jp>
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Hi Geert,

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 RBTX4926 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.

---
Atsushi Nemoto