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Message-Id: <20160126124823.15b08f0a53dd9671fbc685d9@linux-foundation.org>
Date: Tue, 26 Jan 2016 12:48:23 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Dmitry Vyukov <dvyukov@...gle.com>,
Doug Gilbert <dgilbert@...erlog.com>,
David Rientjes <rientjes@...gle.com>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Shiraz Hashim <shashim@...eaurora.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Hugh Dickins <hughd@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
linux-scsi@...r.kernel.org
Subject: Re: mm: VM_BUG_ON_PAGE(PageTail(page)) in mbind
On Tue, 26 Jan 2016 22:28:29 +0200 "Kirill A. Shutemov" <kirill@...temov.name> wrote:
> The patch below fixes the issue for me, but this bug makes me wounder how
> many bugs like this we have in kernel... :-/
>
> Looks like we are too permissive about which VMA is migratable:
> vma_migratable() filters out VMA by VM_IO and VM_PFNMAP.
> I think VM_DONTEXPAND also correlate with VMA which cannot be migrated.
>
> $ git grep VM_DONTEXPAND drivers | grep -v '\(VM_IO\|VM_PFNMAN\)' | wc -l
> 33
>
> Hm.. :-|
>
> It worth looking on them closely... And I wouldn't be surprised if some
> VMAs without all of these flags are not migratable too.
>
> Sigh.. Any thoughts?
Sigh indeed. I think that both VM_DONTEXPAND and VM_DONTDUMP are
pretty good signs that mbind() should not be mucking with this vma. If
such a policy sometimes results in mbind failing to set a policy then
that's not a huge loss - something runs a bit slower maybe.
I mean, we only really expect mbind() to operate against regular old
anon/pagecache memory, yes?
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