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Wed, 12 Aug 2020 06:00:14 -0400 X-MC-Unique: t6Nh71JPPXuTPvtcC0yf2A-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1DE3D8010C7; Wed, 12 Aug 2020 10:00:13 +0000 (UTC) Received: from [10.36.113.2] (ovpn-113-2.ams2.redhat.com [10.36.113.2]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2ADD660BF3; Wed, 12 Aug 2020 10:00:09 +0000 (UTC) Subject: Re: [PATCH V2] mm, page_alloc: fix core hung in free_pcppages_bulk() To: Charan Teja Kalla , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, rientjes@google.com, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, vinmenon@codeaurora.org References: <1597150703-19003-1-git-send-email-charante@codeaurora.org> <848b7d60-2995-d9ae-0055-f3864dece11f@codeaurora.org> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63W5Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAjwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat GmbH Message-ID: Date: Wed, 12 Aug 2020 12:00:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <848b7d60-2995-d9ae-0055-f3864dece11f@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: 80485100E7FD5 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 12.08.20 11:46, Charan Teja Kalla wrote: > > Thanks David for the inputs. > > On 8/12/2020 2:35 AM, David Hildenbrand wrote: >> On 11.08.20 14:58, Charan Teja Reddy wrote: >>> The following race is observed with the repeated online, offline and a >>> delay between two successive online of memory blocks of movable zone. >>> >>> P1 P2 >>> >>> Online the first memory block in >>> the movable zone. The pcp struct >>> values are initialized to default >>> values,i.e., pcp->high = 0 & >>> pcp->batch = 1. >>> >>> Allocate the pages from the >>> movable zone. >>> >>> Try to Online the second memory >>> block in the movable zone thus it >>> entered the online_pages() but yet >>> to call zone_pcp_update(). >>> This process is entered into >>> the exit path thus it tries >>> to release the order-0 pages >>> to pcp lists through >>> free_unref_page_commit(). >>> As pcp->high = 0, pcp->count = 1 >>> proceed to call the function >>> free_pcppages_bulk(). >>> Update the pcp values thus the >>> new pcp values are like, say, >>> pcp->high = 378, pcp->batch = 63. >>> Read the pcp's batch value using >>> READ_ONCE() and pass the same to >>> free_pcppages_bulk(), pcp values >>> passed here are, batch = 63, >>> count = 1. >>> >>> Since num of pages in the pcp >>> lists are less than ->batch, >>> then it will stuck in >>> while(list_empty(list)) loop >>> with interrupts disabled thus >>> a core hung. >>> >>> Avoid this by ensuring free_pcppages_bulk() is called with proper count >>> of pcp list pages. >>> >>> The mentioned race is some what easily reproducible without [1] because >>> pcp's are not updated for the first memory block online and thus there >>> is a enough race window for P2 between alloc+free and pcp struct values >>> update through onlining of second memory block. >>> >>> With [1], the race is still exists but it is very much narrow as we >>> update the pcp struct values for the first memory block online itself. >>> >>> [1]: https://patchwork.kernel.org/patch/11696389/ >>> >> >> IIUC, this is not limited to the movable zone, it could also happen in >> corner cases with the normal zone (e.g., hotplug to a node that only has >> DMA memory, or no other memory yet). > > Yes, this is my understanding too. I explained the above race in terms > of just movable zone for which it is observed. We can add the below line > in the end in patch commit message: > "This is not limited to the movable zone, it could also happen in cases > with the normal zone (e.g., hotplug to a node that only has DMA memory, > or no other memory yet)." Yeah, that makes sense! > > Just curious, there exists such systems where just a dma zone present > and we hot add the normal zone? I am not aware such thing in the > embedded world. You can easily create such setups using QEMU. IIRC, just specify a QEMU guest with 2G initial memory and a single NUMA node, or 4G initial memory and two NUMA nodes. Then hotplug memory. (IIRC kata containers always start a VM with 2G and then hotplug memory) >> >>> Signed-off-by: Charan Teja Reddy >>> --- >>> >>> v1: https://patchwork.kernel.org/patch/11707637/ >>> >>> mm/page_alloc.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index e4896e6..839039f 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -1304,6 +1304,11 @@ static void free_pcppages_bulk(struct zone *zone, int count, >>> struct page *page, *tmp; >>> LIST_HEAD(head); >>> >>> + /* >>> + * Ensure proper count is passed which otherwise would stuck in the >>> + * below while (list_empty(list)) loop. >>> + */ >>> + count = min(pcp->count, count); >>> while (count) { >>> struct list_head *list; >>> >>> >> >> Fixes: and Cc: stable... tags? > > Fixes: 5f8dcc21211a ("page-allocator: split per-cpu list into > one-list-per-migrate-type") > Cc: [2.6+] Did we have memory hotplug support then already? > > I am not sure If I should have to raise V3 including these? Maybe Andrew can fixup when applying. -- Thanks, David / dhildenb