From: Andrea Arcangeli <aarcange@redhat.com>
To: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: v4.6 kernel BUG at mm/rmap.c:1101!
Date: Mon, 23 May 2016 17:08:26 +0200 [thread overview]
Message-ID: <20160523150826.GA20829@redhat.com> (raw)
In-Reply-To: <20160523140638.GA1738@lahna.fi.intel.com>
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.
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.
Can you test this to shut off the false positive?
>From 4db87e3e44837a0b038e58eaa3fea29db84723ec Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Mon, 23 May 2016 17:03:57 +0200
Subject: [PATCH 1/1] mm: thp: avoid false positive VM_BUG_ON_PAGE in
page_move_anon_rmap()
If the page_move_anon_rmap() is refiling a pmd-splitted THP mapped in
a tail page from a pte, the "address" must be THP aligned in order for
the page->index bugcheck to pass in the CONFIG_DEBUG_VM=y builds.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
mm/rmap.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/rmap.c b/mm/rmap.c
index 8a83993..e2e47ba9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1098,7 +1098,10 @@ void page_move_anon_rmap(struct page *page,
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_VMA(!anon_vma, vma);
- VM_BUG_ON_PAGE(page->index != linear_page_index(vma, address), page);
+ VM_BUG_ON_PAGE(page->index !=
+ linear_page_index(vma, PageTransHuge(page) ?
+ address & HPAGE_PMD_MASK :
+ address), page);
anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
/*
next prev parent reply other threads:[~2016-05-23 15:08 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-23 14:06 v4.6 kernel BUG at mm/rmap.c:1101! Mika Westerberg
2016-05-23 14:24 ` Kirill A. Shutemov
2016-05-23 15:18 ` Andrea Arcangeli
2016-05-25 9:47 ` Mika Westerberg
2016-05-23 15:08 ` Andrea Arcangeli [this message]
2016-05-24 8:12 ` Mika Westerberg
2016-05-24 14:08 ` Andrea Arcangeli
2016-05-24 14:53 ` Mika Westerberg
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