Groups > linux.kernel > #1672024

Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c
Date	2017-06-21 23:00 +0200
Message-ID	<tUUTg-2Wi-9@gated-at.bofh.it> (permalink)
References	(2 earlier) <tUSy6-1pG-33@gated-at.bofh.it> <tUTDQ-2a7-3@gated-at.bofh.it> <tUTDQ-2a7-1@gated-at.bofh.it> <tUUqe-2L1-25@gated-at.bofh.it> <tUUzT-2OU-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 06/21, Linus Torvalds wrote:
>
> On Wed, Jun 21, 2017 at 1:27 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > Now __do_page_fault() tries to expand the stack itself, and this check
> > fails.
>
> But we want that check to trigger and cause the access to fail.
> Accessing the stack below the stack pointer is wrong.

I understand. My point is that this check was invalidated by stack-guard-page
a long ago, and this means that we add the user-visible change now.

> Do you have a pointer to the report for this regression? I must have missed it.

See http://marc.info/?t=149794523000001&r=1&w=2

this thread is a bit confusing, the most relevant emails are

	http://marc.info/?l=linux-kernel&m=149806256621440&w=2 (with test case)
	http://marc.info/?l=linux-kernel&m=149806452322233&w=2

Actually, I got another (redhat internal) bug report after this discussion,
and at first glance this is the same thing.

Just in case, I agree that mmap(MAP_GROWSDOWN) is mostly useless, perhaps
we do not even care. But still this is regression.

Oleg.

Thread

Re: [lkp-robot] [mm]  1be7107fbe: kernel_BUG_at_mm/mmap.c Hugh Dickins <hughd@google.com> - 2017-06-21 04:50 +0200
  Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-21 20:30 +0200
    Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-21 21:40 +0200
      Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Oleg Nesterov <oleg@redhat.com> - 2017-06-21 22:30 +0200
        Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-21 22:40 +0200
          Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Oleg Nesterov <oleg@redhat.com> - 2017-06-21 23:00 +0200
            Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-22 00:20 +0200
              Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Hugh Dickins <hughd@google.com> - 2017-06-22 03:10 +0200
                Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Oleg Nesterov <oleg@redhat.com> - 2017-06-22 17:20 +0200
                Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Hugh Dickins <hughd@google.com> - 2017-06-22 20:10 +0200
                Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Oleg Nesterov <oleg@redhat.com> - 2017-06-22 23:00 +0200
    Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Oleg Nesterov <oleg@redhat.com> - 2017-06-21 21:40 +0200
      Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Hugh Dickins <hughd@google.com> - 2017-06-22 06:30 +0200
    Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Hugh Dickins <hughd@google.com> - 2017-06-21 21:50 +0200

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