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Tue, 11 Aug 2020 04:29:28 -0400 X-MC-Unique: 9YMN5odyPpKYFm0ygPpdog-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 43DB71902EA1; Tue, 11 Aug 2020 08:29:27 +0000 (UTC) Received: from [10.36.113.73] (ovpn-113-73.ams2.redhat.com [10.36.113.73]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6CAD66111F; Tue, 11 Aug 2020 08:29:25 +0000 (UTC) Subject: Re: [PATCH] mm, page_alloc: fix core hung in free_pcppages_bulk() To: Charan Teja Reddy , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, vinmenon@codeaurora.org References: <1597075833-16736-1-git-send-email-charante@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: <3b07d2a6-8ce7-5957-8ca5-a8d977852e14@redhat.com> Date: Tue, 11 Aug 2020 10:29:24 +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: <1597075833-16736-1-git-send-email-charante@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Queue-Id: 9FEC9180F8B80 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 10.08.20 18:10, 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. >=20 > P1 P2 >=20 > Online the first memory block in > the movable zone. The pcp struct > values are initialized to default > values,i.e., pcp->high =3D 0 & > pcp->batch =3D 1. >=20 > Allocate the pages from the > movable zone. >=20 > 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 =3D 0, pcp->count =3D 1 > proceed to call the function > free_pcppages_bulk(). > Update the pcp values thus the > new pcp values are like, say, > pcp->high =3D 378, pcp->batch =3D 63. > Read the pcp's batch value using > READ_ONCE() and pass the same to > free_pcppages_bulk(), pcp values > passed here are, batch =3D 63, > count =3D 1. >=20 > 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. >=20 > Avoid this by ensuring free_pcppages_bulk() called with proper count of > pcp list pages. >=20 > 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. >=20 > 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. >=20 > [1]: https://patchwork.kernel.org/patch/11696389/ >=20 > Signed-off-by: Charan Teja Reddy > --- > mm/page_alloc.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) >=20 > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e4896e6..25e7e12 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3106,6 +3106,7 @@ static void free_unref_page_commit(struct page *p= age, unsigned long pfn) > struct zone *zone =3D page_zone(page); > struct per_cpu_pages *pcp; > int migratetype; > + int high; > =20 > migratetype =3D get_pcppage_migratetype(page); > __count_vm_event(PGFREE); > @@ -3128,8 +3129,19 @@ static void free_unref_page_commit(struct page *= page, unsigned long pfn) > pcp =3D &this_cpu_ptr(zone->pageset)->pcp; > list_add(&page->lru, &pcp->lists[migratetype]); > pcp->count++; > - if (pcp->count >=3D pcp->high) { > - unsigned long batch =3D READ_ONCE(pcp->batch); > + high =3D READ_ONCE(pcp->high); > + if (pcp->count >=3D high) { > + int batch; > + > + batch =3D READ_ONCE(pcp->batch); > + /* > + * For non-default pcp struct values, high is always > + * greater than the batch. If high < batch then pass > + * proper count to free the pcp's list pages. > + */ > + if (unlikely(high < batch)) > + batch =3D min(pcp->count, batch); > + > free_pcppages_bulk(zone, batch, pcp); > } > } >=20 I was wondering if we should rather set all pageblocks to MIGRATE_ISOLATE in online_pages() before doing the online_pages_range() call, and do undo_isolate_page_range() after onlining is done. move_pfn_range_to_zone()->memmap_init_zone() marks all pageblocks MIGRATE_MOVABLE, and as that function is used also during boot, we could supply a parameter to configure this. This would prevent another race from happening: Having pages exposed to the buddy ready for allocation in online_pages_range() before the sections are marked online. This would avoid any pages from getting allocated before we're completely done onlining. We would need MIGRATE_ISOLATE/CONFIG_MEMORY_ISOLATION also for CONFIG_MEMORY_HOTPLUG. --=20 Thanks, David / dhildenb