From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Li Wang <liwang@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>,
Janosch Frank <frankja@linux.vnet.ibm.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 3/3] s390/mm: fix mis-accounting of pgtable_bytes
Date: Wed, 31 Oct 2018 07:46:47 +0100 [thread overview]
Message-ID: <20181031074647.32c6e0d7@mschwideX1> (raw)
In-Reply-To: <CAEemH2f2gW22PJYpVrh7p5zJyHOVRfVawJWD+kN3+8LmApePbw@mail.gmail.com>
On Wed, 31 Oct 2018 14:43:38 +0800
Li Wang <liwang@redhat.com> wrote:
> On Wed, Oct 31, 2018 at 2:31 PM, Martin Schwidefsky <schwidefsky@de.ibm.com>
> wrote:
>
> > On Wed, 31 Oct 2018 14:18:33 +0800
> > Li Wang <liwang@redhat.com> wrote:
> >
> > > On Tue, Oct 16, 2018 at 12:42 AM, Martin Schwidefsky <
> > schwidefsky@de.ibm.com
> > > > wrote:
> > >
> > > > In case a fork or a clone system fails in copy_process and the error
> > > > handling does the mmput() at the bad_fork_cleanup_mm label, the
> > > > following warning messages will appear on the console:
> > > >
> > > > BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > >
> > > > The reason for that is the tricks we play with mm_inc_nr_puds() and
> > > > mm_inc_nr_pmds() in init_new_context().
> > > >
> > > > A normal 64-bit process has 3 levels of page table, the p4d level and
> > > > the pud level are folded. On process termination the free_pud_range()
> > > > function in mm/memory.c will subtract 16KB from pgtable_bytes with a
> > > > mm_dec_nr_puds() call, but there actually is not really a pud table.
> > > >
> > > > One issue with this is the fact that pgtable_bytes is usually off
> > > > by a few kilobytes, but the more severe problem is that for a failed
> > > > fork or clone the free_pgtables() function is not called. In this case
> > > > there is no mm_dec_nr_puds() or mm_dec_nr_pmds() that go together with
> > > > the mm_inc_nr_puds() and mm_inc_nr_pmds in init_new_context().
> > > > The pgtable_bytes will be off by 16384 or 32768 bytes and we get the
> > > > BUG message. The message itself is purely cosmetic, but annoying.
> > > >
> > > > To fix this override the mm_pmd_folded, mm_pud_folded and mm_p4d_folded
> > > > function to check for the true size of the address space.
> > > >
> > >
> > > I can confirm that it works to the problem, the warning message is gone
> > > after applying this patch on s390x. And I also done ltp syscalls/cve test
> > > for the patch set on x86_64 arch, there has no new regression.
> > >
> > > Tested-by: Li Wang <liwang@redhat.com>
> >
> > Thanks for testing. Unfortunately Heiko reported another issue yesterday
> > with the patch applied. This time the other way around:
> >
> > BUG: non-zero pgtables_bytes on freeing mm: -16384
> >
>
> Okay, the problem is still triggered by LTP/cve-2017-17052.c?
No, unfortunately we do not have a simple testcase to trigger this new bug.
It happened once with one of our test kernels, the path that leads to this
is completely unclear.
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
next prev parent reply other threads:[~2018-10-31 6:46 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 16:42 [RFC][PATCH 0/3] pgtable bytes mis-accounting v2 Martin Schwidefsky
2018-10-15 16:42 ` [PATCH 1/3] mm: introduce mm_[p4d|pud|pmd]_folded Martin Schwidefsky
2018-10-31 9:02 ` Kirill A. Shutemov
2018-10-31 9:35 ` Martin Schwidefsky
2018-10-31 9:48 ` Kirill A. Shutemov
2018-10-15 16:42 ` [PATCH 2/3] mm: add mm_pxd_folded checks to pgtable_bytes accounting functions Martin Schwidefsky
2018-10-31 9:04 ` Kirill A. Shutemov
2018-10-15 16:42 ` [PATCH 3/3] s390/mm: fix mis-accounting of pgtable_bytes Martin Schwidefsky
[not found] ` <CAEemH2cHNFsiDqPF32K6TNn-XoXCRT0wP4ccAeah4bKHt=FKFA@mail.gmail.com>
2018-10-31 6:31 ` Martin Schwidefsky
[not found] ` <CAEemH2f2gW22PJYpVrh7p5zJyHOVRfVawJWD+kN3+8LmApePbw@mail.gmail.com>
2018-10-31 6:46 ` Martin Schwidefsky [this message]
2018-10-31 9:39 ` Martin Schwidefsky
2018-10-31 10:09 ` Heiko Carstens
2018-10-31 10:36 ` Kirill A. Shutemov
2018-11-27 7:34 ` Heiko Carstens
2018-11-27 8:05 ` Kirill A. Shutemov
2018-11-27 8:13 ` Heiko Carstens
2018-11-27 11:47 ` Guenter Roeck
2018-11-27 11:52 ` Heiko Carstens
2018-11-27 14:31 ` Martin Schwidefsky
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