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Message-ID: <20191011065036.GB30500@hori.linux.bs1.fc.nec.co.jp>
Date: Fri, 11 Oct 2019 06:50:36 +0000
From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To: David Hildenbrand <david@...hat.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized
memmaps in memory_failure()
On Thu, Oct 10, 2019 at 09:17:42AM +0200, David Hildenbrand wrote:
> On 10.10.19 02:26, Naoya Horiguchi wrote:
> > On Wed, Oct 09, 2019 at 04:24:35PM +0200, David Hildenbrand wrote:
> >> We should check for pfn_to_online_page() to not access uninitialized
> >> memmaps. Reshuffle the code so we don't have to duplicate the error
> >> message.
> >>
> >> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> >> Cc: Andrew Morton <akpm@...ux-foundation.org>
> >> Cc: Michal Hocko <mhocko@...nel.org>
> >> Signed-off-by: David Hildenbrand <david@...hat.com>
> >> ---
> >> mm/memory-failure.c | 14 ++++++++------
> >> 1 file changed, 8 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> >> index 7ef849da8278..e866e6e5660b 100644
> >> --- a/mm/memory-failure.c
> >> +++ b/mm/memory-failure.c
> >> @@ -1253,17 +1253,19 @@ int memory_failure(unsigned long pfn, int flags)
> >> if (!sysctl_memory_failure_recovery)
> >> panic("Memory failure on page %lx", pfn);
> >>
> >> - if (!pfn_valid(pfn)) {
> >> + p = pfn_to_online_page(pfn);
> >> + if (!p) {
> >> + if (pfn_valid(pfn)) {
> >> + pgmap = get_dev_pagemap(pfn, NULL);
> >> + if (pgmap)
> >> + return memory_failure_dev_pagemap(pfn, flags,
> >> + pgmap);
> >> + }
> >> pr_err("Memory failure: %#lx: memory outside kernel control\n",
> >> pfn);
> >> return -ENXIO;
> >> }
> >>
> >> - pgmap = get_dev_pagemap(pfn, NULL);
> >> - if (pgmap)
> >> - return memory_failure_dev_pagemap(pfn, flags, pgmap);
> >> -
> >> - p = pfn_to_page(pfn);
> >
> > This change seems to assume that memory_failure_dev_pagemap() is never
> > called for online pages. Is it an intended behavior?
> > Or the concept "online pages" is not applicable to zone device pages?
>
> Yes, that's the real culprit. ZONE_DEVICE/devmem pages are never online
> (SECTION_IS_ONLINE). The terminology "online" only applies to pages that
> were given to the buddy. And as we support sup-section hotadd for
> devmem, we cannot easily make use of the section flag it. I already
> proposed somewhere to convert SECTION_IS_ONLINE to a subsection bitmap
> and call it something like pfn_active().
>
> pfn_online() would then be "pfn_active() && zone != ZONE_DEVICE". And we
> could use pfn_active() everywhere to test for initialized memmaps (well,
> besides some special cases like device reserved memory that does not
> span full sub-sections). Until now, nobody volunteered and I have other
> things to do.
Thank you for explanation. I'm not sure how hard now but we try to do this.
You fix the problem from online/offline viewpoint now, and leave remaining
part untouched. I agree with that approach, and the suggested change looks
good to me.
Acked-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
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