linux-kernel - Re: [PATCH 09/16] sparc64: use the generic get_user_pages

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Date:   Fri, 19 Jul 2019 08:00:53 +0200
From:   Christoph Hellwig <hch@....de>
To:     David Miller <davem@...emloft.net>
Cc:     ldv@...linux.org, hch@....de, khalid.aziz@...cle.com,
        torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
        matorola@...il.com, sparclinux@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/16] sparc64: use the generic get_user_pages_fast code

On Thu, Jul 18, 2019 at 02:14:05PM -0700, David Miller wrote:
> From: "Dmitry V. Levin" <ldv@...linux.org>
> Date: Thu, 18 Jul 2019 00:59:56 +0300
> 
> > So this ended up as commit 7b9afb86b6328f10dc2cad9223d7def12d60e505
> > (thanks to Anatoly for bisecting) and introduced a regression: 
> > futex.test from the strace test suite now causes an Oops on sparc64
> > in futex syscall.
> > 
> > Here is a heavily stripped down reproducer:
> 
> Does not reproduce for me on a T4-2 machine.
> 
> So this problem might depend on the type of system you are on,
> I suspect it's one of those "pre-Niagara vs. Niagara and later"
> situations because that's the dividing line between two set of
> wildly different TLB and cache management methods.
> 
> What kind of machine are you on?

FYI, I'm pretty sure I tested this on Guenthers build test qemu
setup in the end, which further speaks for the different machines
issue.