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[209.132.183.28]) by mx.google.com with ESMTPS id 40si88288qvu.207.2019.01.28.12.03.09 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 28 Jan 2019 12:03:10 -0800 (PST) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CF02B7FD41; Mon, 28 Jan 2019 20:03:08 +0000 (UTC) Received: from [10.36.116.25] (ovpn-116-25.ams2.redhat.com [10.36.116.25]) by smtp.corp.redhat.com (Postfix) with ESMTP id B4C32BA91; Mon, 28 Jan 2019 20:02:53 +0000 (UTC) Subject: Re: [PATCH v1] mm: migrate: don't rely on PageMovable() of newpage after unlocking it To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Mel Gorman , "Kirill A. Shutemov" , Michal Hocko , Naoya Horiguchi , Jan Kara , Andrea Arcangeli , Dominik Brodowski , Matthew Wilcox , Vratislav Bendel , Rafael Aquini , Konstantin Khlebnikov , Minchan Kim , stable@vger.kernel.org References: <20190128160403.16657-1-david@redhat.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: Mon, 28 Jan 2019 21:02:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20190128160403.16657-1-david@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Mon, 28 Jan 2019 20:03:09 +0000 (UTC) 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 28.01.19 17:04, David Hildenbrand wrote: > While debugging some crashes related to virtio-balloon deflation that > happened under the old balloon migration code, I stumbled over a race > that still exists today. > > What we experienced: > > drivers/virtio/virtio_balloon.c:release_pages_balloon(): > - WARNING: CPU: 13 PID: 6586 at lib/list_debug.c:59 __list_del_entry+0xa1/0xd0 > - list_del corruption. prev->next should be ffffe253961090a0, but was dead000000000100 > > Turns out after having added the page to a local list when dequeuing, > the page would suddenly be moved to an LRU list before we would free it > via the local list, corrupting both lists. So a page we own and that is > !LRU was moved to an LRU list. > > In __unmap_and_move(), we lock the old and newpage and perform the > migration. In case of vitio-balloon, the new page will become > movable, the old page will no longer be movable. > > However, after unlocking newpage, there is nothing stopping the newpage > from getting dequeued and freed by virtio-balloon. This > will result in the newpage > 1. No longer having PageMovable() > 2. Getting moved to the local list before finally freeing it (using > page->lru) > > Back in the migration thread in __unmap_and_move(), we would after > unlocking the newpage suddenly no longer have PageMovable(newpage) and > will therefore call putback_lru_page(newpage), modifying page->lru > although that list is still in use by virtio-balloon. > > To summarize, we have a race between migrating the newpage and checking > for PageMovable(newpage). Instead of checking PageMovable(newpage), we > can simply rely on is_lru of the original page. > > Looks like this was introduced by d6d86c0a7f8d ("mm/balloon_compaction: > redesign ballooned pages management"), which was backported up to 3.12. > Old compaction code used PageBalloon() via -_is_movable_balloon_page() > instead of PageMovable(), however with the same semantics. > > Cc: Andrew Morton > Cc: Mel Gorman > Cc: "Kirill A. Shutemov" > Cc: Michal Hocko > Cc: Naoya Horiguchi > Cc: Jan Kara > Cc: Andrea Arcangeli > Cc: Dominik Brodowski > Cc: Matthew Wilcox > Cc: Vratislav Bendel > Cc: Rafael Aquini > Cc: Konstantin Khlebnikov > Cc: Minchan Kim > Cc: stable@vger.kernel.org # 3.12+ > Fixes: d6d86c0a7f8d ("mm/balloon_compaction: redesign ballooned pages management") > Reported-by: Vratislav Bendel > Acked-by: Michal Hocko > Acked-by: Rafael Aquini > Signed-off-by: David Hildenbrand > --- > mm/migrate.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 4512afab46ac..31e002270b05 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1135,10 +1135,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage, > * If migration is successful, decrease refcount of the newpage > * which will not free the page because new page owner increased > * refcounter. As well, if it is LRU page, add the page to LRU > - * list in here. > + * list in here. Don't rely on PageMovable(newpage), as that could > + * already have changed after unlocking newpage (e.g. > + * virtio-balloon deflation). > */ > if (rc == MIGRATEPAGE_SUCCESS) { > - if (unlikely(__PageMovable(newpage))) > + if (unlikely(!is_lru)) > put_page(newpage); > else > putback_lru_page(newpage); > Vratislav just pointed out that this issue should not happen on upstream as __PageMovable(newpage) will still return true even after __ClearPageMovable(newpage). Only PageMovable(newpage) would actually return false. (not sure if I am happy about this, this is horribly confusing and complicated) I am not 100% sure yet, but I guess Vratislav is right. So it was effectively fixed by b1123ea6d3b3 ("mm: balloon: use general non-lru movable page feature"), which checks for __PageMovable(newpage) instead of __is_movable_balloon_page(newpage). Anybody wanting to fix stable kernels either has to backport something proposed in this patch or b1123ea6d3b3. -- Thanks, David / dhildenb