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From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Michal Hocko <mhocko@kernel.org>
Cc: Joel Stanley <joel@jms.id.au>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: linux-next: Tree for Nov 7
Date: Mon, 13 Nov 2017 15:09:09 +0000
Message-ID: <20171113150908.GL12318@n2100.armlinux.org.uk> (raw)
In-Reply-To: <20171113141140.cns5fxt5jg4zdedb@dhcp22.suse.cz>

On Mon, Nov 13, 2017 at 03:11:40PM +0100, Michal Hocko wrote:
> On Mon 13-11-17 10:20:06, Michal Hocko wrote:
> > [Cc arm and ppc maintainers]
> > 
> > Thanks a lot for testing!
> > 
> > On Sun 12-11-17 11:38:02, Joel Stanley wrote:
> > > On Fri, Nov 10, 2017 at 11:00 PM, Michal Hocko <mhocko@kernel.org> wrote:
> > > > Hi Joel,
> > > >
> > > > On Wed 08-11-17 15:20:50, Michal Hocko wrote:
> > > > [...]
> > > >> > There are a lot of messages on the way up that look like this:
> > > >> >
> > > >> > [    2.527460] Uhuuh, elf segement at 000d9000 requested but the
> > > >> > memory is mapped already
> > > >> > [    2.540160] Uhuuh, elf segement at 000d9000 requested but the
> > > >> > memory is mapped already
> > > >> > [    2.546153] Uhuuh, elf segement at 000d9000 requested but the
> > > >> > memory is mapped already
> > > >> >
> > > >> > And then trying to run userspace looks like this:
> > > >>
> > > >> Could you please run with debugging patch posted
> > > >> http://lkml.kernel.org/r/20171107102854.vylrtaodla63kc57@dhcp22.suse.cz
> > > >
> > > > Did you have chance to test with this debugging patch, please?
> > > 
> > > Lots of this:
> > > 
> > > [    1.177266] Uhuuh, elf segement at 000d9000 requested but the  memory is mapped already, got 000dd000
> > > [    1.177555] Clashing vma [dd000, de000] flags:100873 name:(null)
> > 
> > This smells like the problem I've expected that mmap with hint doesn't
> > respect the hint even though there is no clashing mapping. The above
> > basically says that we didn't map at 0xd9000 but it has placed it at
> > 0xdd000. The nearest (clashing) vma is at 0xdd000 so this is our new
> > mapping. find_vma returns the closest vma (with addr < vm_end) for the
> > given address 0xd9000 so this address cannot be mapped by any other vma.
> > 
> > Now that I am looking at arm's arch_get_unmapped_area it does perform
> > aligning for shared vmas.
> 
> Sorry for confusion here. These are not shared mappings as pointed out
> by Russell in a private email. I got confused by the above flags which I
> have misinterpreted as bit 0 set => MAP_SHARED. These are vm_flags
> obviously so the bit 0 is VM_READ. Sorry about the confusion. The real
> reason we are doing the alignment is that we do a file mapping
> 	/*
> 	 * We only need to do colour alignment if either the I or D
> 	 * caches alias.
> 	 */
> 	if (aliasing)
> 		do_align = filp || (flags & MAP_SHARED);
> 
> I am not really familiar with this architecture to understand why do we
> need aliasing for file mappings, though.

I think it's there so that flush_dcache_page() works - possibly
get_user_pages() being used on a private mapping of page cache pages,
but that's guessing.

I'm afraid I don't remember all the details, this is code from around
15 years ago, and I'd be very nervous about changing it now without
fully understanding the issues.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up
According to speedtest.net: 8.21Mbps down 510kbps up

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-07  5:22 Stephen Rothwell
2017-11-07 22:22 ` Joel Stanley
2017-11-08 14:20   ` Michal Hocko
2017-11-10 12:30     ` Michal Hocko
2017-11-12  1:08       ` Joel Stanley
2017-11-13  9:20         ` Michal Hocko
2017-11-13  9:34           ` Russell King - ARM Linux
2017-11-13  9:42           ` Michal Hocko
2017-11-13 11:34             ` Michael Ellerman
2017-11-13 12:00               ` Michal Hocko
2017-11-13 15:16                 ` Michal Hocko
2017-11-13 15:48                   ` Russell King - ARM Linux
2017-11-13 15:59                     ` Michal Hocko
2017-11-13 15:49                   ` Michal Hocko
2017-11-13 16:06                     ` Michal Hocko
2017-11-13 16:35                       ` Khalid Aziz
2017-11-14  7:07                         ` Michal Hocko
2017-11-14  9:18                       ` Michael Ellerman
2017-11-14  9:29                         ` Michal Hocko
2017-11-14  9:02                   ` Michael Ellerman
2017-11-14  8:54                 ` Michael Ellerman
2017-11-14  9:04                   ` Michal Hocko
2017-11-14 14:52                     ` Khalid Aziz
2017-11-13 14:11           ` Michal Hocko
2017-11-13 15:09             ` Russell King - ARM Linux [this message]
2017-11-13 15:31               ` Michal Hocko
2017-11-14  0:03         ` Andrew Morton
2017-11-14  0:36           ` Stephen Rothwell
  -- strict thread matches above, loose matches on Subject: below --
2019-11-07  8:07 Stephen Rothwell
2018-11-07  3:16 Stephen Rothwell
2013-11-07  7:31 Stephen Rothwell
2012-11-07  5:15 Stephen Rothwell

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