linux-kernel - Re: 3.15-rc8 oops in copy_page

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Message-ID: <CA+55aFxiOsceOsm7zYyvFAxDF3=gxUXj=_61Nce3VkELfJr7cg@mail.gmail.com>
Date:	Fri, 6 Jun 2014 11:26:14 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: 3.15-rc8 oops in copy_page_rep after page fault.

On Fri, Jun 6, 2014 at 10:43 AM, Dave Jones <davej@...hat.com> wrote:
>
> RIP: 0010:[<ffffffff8b3287b5>]  [<ffffffff8b3287b5>] copy_page_rep+0x5/0x10

Ok, it's the first iteration of "rep movsq" (%rcx is still 0x200) for
copying a page, and the pages are

  RSI: ffff880052766000
  RDI: ffff880014efe000

which both look like reasonable kernel addresses. So I'm assuming it's
DEBUG_PAGEALLOC that makes this trigger, and since the error code is
0, and the CR2 value matches RSI, it's the source page that seems to
have been freed.

And I see absolutely _zero_ reason for wht your 64k mmap_min_addr
should make any difference what-so-ever. That's just odd.

Anyway, can you try to figure out _which_ copy_user_highpage() it is
(by looking at what is around the call-site at
"handle_mm_fault+0x1e0". The fact that we have a stale
do_huge_pmd_wp_page() on the stack makes me suspect that we have hit
that VM_FAULT_FALLBACK case and this is related to splitting. Adding a
few more people explicitly to the cc in case anybody sees anything
(original email on lkml and linux-mm for context, guys).

            Linus
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