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From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
	kernel test robot <xiaolong.ye@intel.com>,
	Michal Hocko <mhocko@suse.com>,
	LKML <linux-kernel@vger.kernel.org>, LKP <lkp@01.org>
Subject: Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c
Date: Wed, 21 Jun 2017 22:56:17 +0200	[thread overview]
Message-ID: <20170621205617.GA29841@redhat.com> (raw)
In-Reply-To: <CA+55aFyupxx0K6SCi5_vd5nt0FmUYrYGF6yB+k9F+9zbgMwsiQ@mail.gmail.com>

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.

WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: lkp@lists.01.org
Subject: Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c
Date: Wed, 21 Jun 2017 22:56:17 +0200	[thread overview]
Message-ID: <20170621205617.GA29841@redhat.com> (raw)
In-Reply-To: <CA+55aFyupxx0K6SCi5_vd5nt0FmUYrYGF6yB+k9F+9zbgMwsiQ@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 1078 bytes --]

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.


  reply	other threads:[~2017-06-21 20:56 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-21  2:35 [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c kernel test robot
2017-06-21  2:35 ` kernel test robot
2017-06-21  2:41 ` Hugh Dickins
2017-06-21  2:41   ` Hugh Dickins
2017-06-21 18:29   ` Linus Torvalds
2017-06-21 18:29     ` Linus Torvalds
2017-06-21 19:33     ` Oleg Nesterov
2017-06-21 19:33       ` Oleg Nesterov
2017-06-21 19:39       ` Linus Torvalds
2017-06-21 19:39         ` Linus Torvalds
2017-06-21 20:27         ` Oleg Nesterov
2017-06-21 20:27           ` Oleg Nesterov
2017-06-21 20:30           ` Linus Torvalds
2017-06-21 20:30             ` Linus Torvalds
2017-06-21 20:56             ` Oleg Nesterov [this message]
2017-06-21 20:56               ` Oleg Nesterov
2017-06-21 22:19               ` Linus Torvalds
2017-06-21 22:19                 ` Linus Torvalds
2017-06-22  1:07                 ` Hugh Dickins
2017-06-22  1:07                   ` Hugh Dickins
2017-06-22 10:58                   ` Dmitry Safonov
2017-06-22 10:58                     ` Dmitry Safonov
2017-06-22 15:16                   ` Oleg Nesterov
2017-06-22 15:16                     ` Oleg Nesterov
2017-06-22 18:04                     ` Hugh Dickins
2017-06-22 18:04                       ` Hugh Dickins
2017-06-22 20:51                       ` Oleg Nesterov
2017-06-22 20:51                         ` Oleg Nesterov
2017-06-22  4:23       ` Hugh Dickins
2017-06-22  4:23         ` Hugh Dickins
2017-06-21 19:39     ` Hugh Dickins
2017-06-21 19:39       ` Hugh Dickins

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