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Date:   Mon, 13 Nov 2017 15:11:40 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Joel Stanley <joel@jms.id.au>
Cc:     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>,
        Russell King <linux@armlinux.org.uk>,
        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
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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.
-- 
Michal Hocko
SUSE Labs

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