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[2003:cb:c74b:d000:3a9:de5c:9ae6:ccb3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432dac216a4sm193824675e9.44.2024.11.19.06.33.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Nov 2024 06:33:18 -0800 (PST) Message-ID: <64d5e357-94b5-48b4-b6cf-0a7a578f82ae@redhat.com> Date: Tue, 19 Nov 2024 15:33:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: handle NULL pages in unpin_user_pages() To: John Hubbard , Andrew Morton Cc: LKML , linux-mm@kvack.org, Oscar Salvador , Vivek Kasireddy , Dave Airlie , Gerd Hoffmann , Matthew Wilcox , Christoph Hellwig , Jason Gunthorpe , Peter Xu , Arnd Bergmann , Daniel Vetter , Dongwon Kim , Hugh Dickins , Junxiao Chang , stable@vger.kernel.org References: <20241119044923.194853-1-jhubbard@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW 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/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/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 In-Reply-To: <20241119044923.194853-1-jhubbard@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ISsL8E2HxzfLmSm4d4K6OdAxHajVyNSIsxl1ORB9pAU_1732026801 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 0043040009 X-Stat-Signature: neygwprmuw3o83gdu37nnf7it8mkrsjd X-HE-Tag: 1732026764-991083 X-HE-Meta: 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 PUVSHT27 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 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: List-Subscribe: List-Unsubscribe: On 19.11.24 05:49, John Hubbard wrote: > The recent addition of "pofs" (pages or folios) handling to gup has a > flaw: it assumes that unpin_user_pages() handles NULL pages in the > pages** array. That's not the case, as I discovered when I ran on a new > configuration on my test machine. > > Fix this by skipping NULL pages in unpin_user_pages(), just like > unpin_folios() already does. > > Details: when booting on x86 with "numa=fake=2 movablecore=4G" on Linux > 6.12, and running this: > > tools/testing/selftests/mm/gup_longterm > > ...I get the following crash: > > BUG: kernel NULL pointer dereference, address: 0000000000000008 > RIP: 0010:sanity_check_pinned_pages+0x3a/0x2d0 > ... > Call Trace: > > ? __die_body+0x66/0xb0 > ? page_fault_oops+0x30c/0x3b0 > ? do_user_addr_fault+0x6c3/0x720 > ? irqentry_enter+0x34/0x60 > ? exc_page_fault+0x68/0x100 > ? asm_exc_page_fault+0x22/0x30 > ? sanity_check_pinned_pages+0x3a/0x2d0 > unpin_user_pages+0x24/0xe0 > check_and_migrate_movable_pages_or_folios+0x455/0x4b0 > __gup_longterm_locked+0x3bf/0x820 > ? mmap_read_lock_killable+0x12/0x50 > ? __pfx_mmap_read_lock_killable+0x10/0x10 > pin_user_pages+0x66/0xa0 > gup_test_ioctl+0x358/0xb20 > __se_sys_ioctl+0x6b/0xc0 > do_syscall_64+0x7b/0x150 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Fixes: 94efde1d1539 ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases") > Cc: David Hildenbrand > Cc: Oscar Salvador > Cc: Vivek Kasireddy > Cc: Dave Airlie > Cc: Gerd Hoffmann > Cc: Matthew Wilcox > Cc: Christoph Hellwig > Cc: Jason Gunthorpe > Cc: Peter Xu > Cc: Arnd Bergmann > Cc: Daniel Vetter > Cc: Dongwon Kim > Cc: Hugh Dickins > Cc: Junxiao Chang > Cc: > Signed-off-by: John Hubbard > --- > > Hi, > > I got a nasty shock when I tried out a new test machine setup last > night--I wish I'd noticed the problem earlier! But anyway, this should > make it all better... > > I've asked Greg K-H to hold off on including commit 94efde1d1539 > ("mm/gup: avoid an unnecessary allocation call for FOLL_LONGTERM cases") > in linux-stable (6.11.y), but if this fix-to-the-fix looks good, then > maybe both fixes can ultimately end up in stable. > Ouch! > thanks, > John Hubbard > > mm/gup.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index ad0c8922dac3..6e417502728a 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -52,7 +52,12 @@ static inline void sanity_check_pinned_pages(struct page **pages, > */ > for (; npages; npages--, pages++) { > struct page *page = *pages; > - struct folio *folio = page_folio(page); > + struct folio *folio; > + > + if (!page) > + continue; > + > + folio = page_folio(page); > > if (is_zero_page(page) || > !folio_test_anon(folio)) > @@ -248,9 +253,14 @@ static inline struct folio *gup_folio_range_next(struct page *start, > static inline struct folio *gup_folio_next(struct page **list, > unsigned long npages, unsigned long i, unsigned int *ntails) > { > - struct folio *folio = page_folio(list[i]); > + struct folio *folio; > unsigned int nr; > > + if (!list[i]) > + return NULL; > + I don't particularly enjoy returning NULL here, if we don't teach the other users of that function about that possibility. There are two other users. Also: we are not setting "ntails" to 1. I think the callers uses that as "nr" to advance npages. So the caller has to make sure to set "nr = 1" in case it sees "NULL". Alternatively ... > + folio = page_folio(list[i]); > + > for (nr = i + 1; nr < npages; nr++) { > if (page_folio(list[nr]) != folio) > break; > @@ -410,6 +420,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages) > sanity_check_pinned_pages(pages, npages); > for (i = 0; i < npages; i += nr) { ... handle it here if (!pages[i]) { nr = 1; continue; } No strong opinion. But I think we should either update all callers to deal with returning NULL from this function, and set "nr = 1". -- Cheers, David / dhildenb