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Message-ID: <20160524081223.GE1712@lahna.fi.intel.com> Date: Tue, 24 May 2016 11:12:23 +0300 From: Mika Westerberg <mika.westerberg@...ux.intel.com> To: Andrea Arcangeli <aarcange@...hat.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, linux-kernel@...r.kernel.org Subject: Re: v4.6 kernel BUG at mm/rmap.c:1101! On Mon, May 23, 2016 at 05:08:26PM +0200, Andrea Arcangeli wrote: > On Mon, May 23, 2016 at 05:06:38PM +0300, Mika Westerberg wrote: > > Hi, > > > > After upgrading kernel of my desktop system from v4.6-rc7 to v4.6, I've > > started seeing following: > > > > [176611.093747] page:ffffea0000360000 count:1 mapcount:0 mapping:ffff880034d2e0a1 index:0x1f9b06600 compound_mapcount: 0 > > [176611.093751] flags: 0x3fff8000044079(locked|uptodate|dirty|lru|active|head|swapbacked) > > [176611.093752] page dumped because: VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address)) > > [176611.093753] page->mem_cgroup:ffff88049e81b800 > > [176611.093765] ------------[ cut here ]------------ > > This is a splitted pmd tail that is triggering a COW, but it's still a > compound page because the physical split didn't happen yet. > > So like Kirill correctly pointed out, in such case we've to do > compound_head because the page->mapping that has to be refiled to the > local anon_vma is in the head. > > It's just a false positive VM_BUG_ON, the code itself is correct. OK, thanks for the explanation. > Production kernels should be built with CONFIG_DEBUG_VM=n so this is > not going to affect them and there's no bug for the production builds. Hmm, the kernel shipped with Fedora 23 has that enabled: lahna % grep CONFIG_DEBUG_VM /boot/config-4.4.9-300.fc23.x86_64 CONFIG_DEBUG_VM=y # CONFIG_DEBUG_VM_VMACACHE is not set # CONFIG_DEBUG_VM_RB is not set > Can you test this to shut off the false positive? I'm testing with Kirill's patch (because he sent it first ;-)) and let you know what happens. Thanks!
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