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Thu, 26 Sep 2019 09:22:54 +0000 (UTC) Received: from [10.36.117.220] (ovpn-117-220.ams2.redhat.com [10.36.117.220]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7BB6D6062A; Thu, 26 Sep 2019 09:22:52 +0000 (UTC) Subject: Re: [PATCH v4 2/8] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span() To: "Aneesh Kumar K.V" , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Oscar Salvador , Michal Hocko , Pavel Tatashin , Dan Williams References: <20190830091428.18399-1-david@redhat.com> <20190830091428.18399-3-david@redhat.com> <87wodvo1yl.fsf@linux.ibm.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: Date: Thu, 26 Sep 2019 11:22:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <87wodvo1yl.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.71]); Thu, 26 Sep 2019 09:22:54 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 26.09.19 11:12, Aneesh Kumar K.V wrote: > David Hildenbrand writes: >=20 >> Let's limit shrinking to !ZONE_DEVICE so we can fix the current code. = We >> should never try to touch the memmap of offline sections where we coul= d >> have uninitialized memmaps and could trigger BUGs when calling >> page_to_nid() on poisoned pages. >> >> Stopping to shrink the ZONE_DEVICE is fine as set_zone_contiguous() ca= nnot >> deal with ZONE_DEVICE either way. The zones will always be !contiguous >> already and zone shrinking is therefore of limited use. >=20 > Can you add more details w.r.t ZONE_DEVICE? I can convert that to "There is no reliable way to distinguish an uninitialized memmap from an initialized memmap that belongs to ZONE_DEVICE, as we don't have anything like SECTION_IS_ONLINE we can use similar to pfn_to_online_section() for !ZONE_DEVICE memory. E.g., set_zone_contiguous() similarly relies on pfn_to_online_section() and will therefore never set a ZONE_DEVICE zone consecutive. Stopping to shrink the ZONE_DEVICE therefore results in no observable changes, besides /proc/zoneinfo indicating different boundaries - something we can totally live with." >=20 >> >> Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory >> hotplug"), the memmap was initialized with 0 and the node with the >> right value. So the zone might be wrong but not garbage. After that >> commit, both the zone and the node will be garbage when touching >> uninitialized memmaps. >> >> Cc: Andrew Morton >> Cc: Oscar Salvador >> Cc: David Hildenbrand >> Cc: Michal Hocko >> Cc: Pavel Tatashin >> Cc: Dan Williams >> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug") >> Reported-by: Aneesh Kumar K.V >> Signed-off-by: David Hildenbrand >> --- >> mm/memory_hotplug.c | 14 +++++++++++--- >> 1 file changed, 11 insertions(+), 3 deletions(-) >> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index ddba8d786e4a..e0d1f6a9dfeb 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -331,7 +331,7 @@ static unsigned long find_smallest_section_pfn(int= nid, struct zone *zone, >> unsigned long end_pfn) >> { >> for (; start_pfn < end_pfn; start_pfn +=3D PAGES_PER_SUBSECTION) { >> - if (unlikely(!pfn_valid(start_pfn))) >> + if (unlikely(!pfn_to_online_page(start_pfn))) >> continue; >> =20 >> if (unlikely(pfn_to_nid(start_pfn) !=3D nid)) >> @@ -356,7 +356,7 @@ static unsigned long find_biggest_section_pfn(int = nid, struct zone *zone, >> /* pfn is the end pfn of a memory section. */ >> pfn =3D end_pfn - 1; >> for (; pfn >=3D start_pfn; pfn -=3D PAGES_PER_SUBSECTION) { >> - if (unlikely(!pfn_valid(pfn))) >> + if (unlikely(!pfn_to_online_page(pfn))) >> continue; >> =20 >> if (unlikely(pfn_to_nid(pfn) !=3D nid)) >> @@ -415,7 +415,7 @@ static void shrink_zone_span(struct zone *zone, un= signed long start_pfn, >> */ >> pfn =3D zone_start_pfn; >> for (; pfn < zone_end_pfn; pfn +=3D PAGES_PER_SUBSECTION) { >> - if (unlikely(!pfn_valid(pfn))) >> + if (unlikely(!pfn_to_online_page(pfn))) >> continue; >> =20 >> if (page_zone(pfn_to_page(pfn)) !=3D zone) >> @@ -463,6 +463,14 @@ static void __remove_zone(struct zone *zone, unsi= gned long start_pfn, >> struct pglist_data *pgdat =3D zone->zone_pgdat; >> unsigned long flags; >> =20 >> + /* >> + * Zone shrinking code cannot properly deal with ZONE_DEVICE. So >> + * we will not try to shrink the zones - which is okay as >> + * set_zone_contiguous() cannot deal with ZONE_DEVICE either way. >> + */ >> + if (zone_idx(zone) =3D=3D ZONE_DEVICE) >> + return; >=20 > Can you describe here what is special about ZONE_DEVICE? I think adding more details to the description is sufficient, especially as this also applies to set_zone_contiguous(). Thanks! --=20 Thanks, David / dhildenb