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

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Date:   Thu, 18 Jul 2019 00:59:56 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Christoph Hellwig <hch@....de>,
        Khalid Aziz <khalid.aziz@...cle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Anatoly Pugachev <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

Hi,

On Tue, Jun 25, 2019 at 04:37:08PM +0200, Christoph Hellwig wrote:
> The sparc64 code is mostly equivalent to the generic one, minus various
> bugfixes and two arch overrides that this patch adds to pgtable.h.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>
> ---
>  arch/sparc/Kconfig                  |   1 +
>  arch/sparc/include/asm/pgtable_64.h |  18 ++
>  arch/sparc/mm/Makefile              |   2 +-
>  arch/sparc/mm/gup.c                 | 340 ----------------------------
>  4 files changed, 20 insertions(+), 341 deletions(-)
>  delete mode 100644 arch/sparc/mm/gup.c

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:

// SPDX-License-Identifier: GPL-2.0-or-later
#include <err.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <asm/unistd.h>
int main(void)
{
	size_t page_size = sysconf(_SC_PAGESIZE);
	size_t alloc_size = 3 * page_size;
	void *p = mmap(NULL, alloc_size, PROT_READ | PROT_WRITE,
		       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	if (MAP_FAILED == p)
		err(EXIT_FAILURE, "mmap(%zu)", alloc_size);
	void *hole = p + page_size;
	if (munmap(hole, page_size))
		err(EXIT_FAILURE, "munmap(%p, %zu)", hole, page_size);
	syscall(__NR_futex, (unsigned long) hole, 0L, 0L, 0L, 0L, 0L);
	return 0;
}

-- 
ldv

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