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[2003:cb:c705:7600:62cc:24c1:9dbe:a2f5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37d7fa87b5dsm6554293f8f.40.2024.10.17.01.53.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Oct 2024 01:53:55 -0700 (PDT) Message-ID: <9a2232d6-74c4-426f-bfab-668c5c5ad143@redhat.com> Date: Thu, 17 Oct 2024 10:53:54 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: stop leaking pinned pages in low memory conditions From: David Hildenbrand To: John Hubbard , Andrew Morton Cc: LKML , linux-mm@kvack.org, Alistair Popple , Shigeru Yoshida , Jason Gunthorpe , Minchan Kim , Pasha Tatashin References: <20241016202242.456953-1-jhubbard@nvidia.com> <1f8dcae1-416e-43cf-8dda-5440e0db4c00@redhat.com> Content-Language: en-US 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: <1f8dcae1-416e-43cf-8dda-5440e0db4c00@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.10.24 10:51, David Hildenbrand wrote: > On 16.10.24 22:22, John Hubbard wrote: >> If a driver tries to call any of the pin_user_pages*(FOLL_LONGTERM) >> family of functions, and requests "too many" pages, then the call will >> erroneously leave pages pinned. This is visible in user space as an >> actual memory leak. >> >> Repro is trivial: just make enough pin_user_pages(FOLL_LONGTERM) calls >> to exhaust memory. >> >> The root cause of the problem is this sequence, within >> __gup_longterm_locked(): >> >> __get_user_pages_locked() >> rc = check_and_migrate_movable_pages() >> >> ...which gets retried in a loop. The loop error handling is incomplete, >> clearly due to a somewhat unusual and complicated tri-state error API. >> But anyway, if -ENOMEM, or in fact, any unexpected error is returned >> from check_and_migrate_movable_pages(), then __gup_longterm_locked() >> happily returns the error, while leaving the pages pinned. >> >> In the failed case, which is an app that requests (via a device driver) >> 30720000000 bytes to be pinned, and then exits, I see this: >> >> $ grep foll /proc/vmstat >> nr_foll_pin_acquired 7502048 >> nr_foll_pin_released 2048 >> >> And after applying this patch, it returns to balanced pins: >> >> $ grep foll /proc/vmstat >> nr_foll_pin_acquired 7502048 >> nr_foll_pin_released 7502048 >> >> Fix this by unpinning the pages that __get_user_pages_locked() has >> pinned, in such error cases. >> >> Fixes: 24a95998e9ba ("mm/gup.c: simplify and fix check_and_migrate_movable_pages() return codes") >> Cc: Alistair Popple >> Cc: Shigeru Yoshida >> Cc: David Hildenbrand >> Cc: Jason Gunthorpe >> Cc: Minchan Kim >> Cc: Pasha Tatashin >> Signed-off-by: John Hubbard >> --- >> mm/gup.c | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index a82890b46a36..24acf53c8294 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -2492,6 +2492,17 @@ static long __gup_longterm_locked(struct mm_struct *mm, >> >> /* FOLL_LONGTERM implies FOLL_PIN */ >> rc = check_and_migrate_movable_pages(nr_pinned_pages, pages); >> + >> + /* >> + * The __get_user_pages_locked() call happens before we know >> + * that whether it's possible to successfully complete the whole >> + * operation. To compensate for this, if we get an unexpected >> + * error (such as -ENOMEM) then we must unpin everything, before >> + * erroring out. >> + */ >> + if (rc != -EAGAIN && rc != 0) >> + unpin_user_pages(pages, nr_pinned_pages); >> + >> } while (rc == -EAGAIN); > > Wouldn't it be cleaner to simply have here after the loop (possibly even > after the memalloc_pin_restore()) > > if (rc) > unpin_user_pages(pages, nr_pinned_pages); > > But maybe I am missing something. And staring at memfd_pin_folios(), don't we have the same issue there if check_and_migrate_movable_folios() fails? diff --git a/mm/gup.c b/mm/gup.c index a82890b46a36..f79974d38608 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -3708,12 +3708,10 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end, ret = check_and_migrate_movable_folios(nr_folios, folios); } while (ret == -EAGAIN); - memalloc_pin_restore(flags); - return ret ? ret : nr_folios; err: memalloc_pin_restore(flags); - unpin_folios(folios, nr_folios); - - return ret; + if (ret) + unpin_folios(folios, nr_folios); + return ret ? ret : nr_folios; } EXPORT_SYMBOL_GPL(memfd_pin_folios); -- Cheers, David / dhildenb