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(p200300cbc7398e007a461b8c8b130d3d.dip0.t-ipconnect.de. [2003:cb:c739:8e00:7a46:1b8c:8b13:d3d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-381ed99a0efsm15178034f8f.58.2024.11.12.03.10.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Nov 2024 03:10:23 -0800 (PST) Message-ID: Date: Tue, 12 Nov 2024 12:10:20 +0100 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 v3 2/8] binder: concurrent page installation To: Carlos Llamas , Greg Kroah-Hartman , =?UTF-8?Q?Arve_Hj=C3=B8nnev=C3=A5g?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Christian Brauner , Suren Baghdasaryan Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, Barry Song , "Liam R. Howlett" References: <20241108191057.3288442-1-cmllamas@google.com> <20241108191057.3288442-3-cmllamas@google.com> From: David Hildenbrand 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: <20241108191057.3288442-3-cmllamas@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 08.11.24 20:10, Carlos Llamas wrote: > Allow multiple callers to install pages simultaneously by downgrading > the mmap_sem to non-exclusive mode. Races to the same PTE are handled > using get_user_pages_remote() to retrieve the already installed page. > This method significantly reduces contention in the mmap semaphore. > > To ensure safety, vma_lookup() is used (instead of alloc->vma) to avoid > operating on an isolated VMA. In addition, zap_page_range_single() is > called under the alloc->mutex to avoid racing with the shrinker. > > Many thanks to Barry Song who posted a similar approach [1]. > > Link: https://lore.kernel.org/all/20240902225009.34576-1-21cnbao@gmail.com/ [1] > Cc: David Hildenbrand > Cc: Barry Song > Cc: Suren Baghdasaryan > Cc: Liam R. Howlett > Reviewed-by: Suren Baghdasaryan > Signed-off-by: Carlos Llamas > --- > drivers/android/binder_alloc.c | 64 +++++++++++++++++++++------------- > 1 file changed, 40 insertions(+), 24 deletions(-) > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c > index 7241bf4a3ff2..2ab520c285b3 100644 > --- a/drivers/android/binder_alloc.c > +++ b/drivers/android/binder_alloc.c > @@ -221,26 +221,14 @@ static int binder_install_single_page(struct binder_alloc *alloc, > struct binder_lru_page *lru_page, > unsigned long addr) > { > + struct vm_area_struct *vma; > struct page *page; > - int ret = 0; > + long npages; > + int ret; > > if (!mmget_not_zero(alloc->mm)) > return -ESRCH; > > - /* > - * Protected with mmap_sem in write mode as multiple tasks > - * might race to install the same page. > - */ > - mmap_write_lock(alloc->mm); > - if (binder_get_installed_page(lru_page)) > - goto out; > - > - if (!alloc->vma) { > - pr_err("%d: %s failed, no vma\n", alloc->pid, __func__); > - ret = -ESRCH; > - goto out; > - } > - > page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO); > if (!page) { > pr_err("%d: failed to allocate page\n", alloc->pid); > @@ -248,19 +236,47 @@ static int binder_install_single_page(struct binder_alloc *alloc, > goto out; > } > > - ret = vm_insert_page(alloc->vma, addr, page); > - if (ret) { > + mmap_read_lock(alloc->mm); > + vma = vma_lookup(alloc->mm, addr); > + if (!vma || vma != alloc->vma) { > + __free_page(page); > + pr_err("%d: %s failed, no vma\n", alloc->pid, __func__); > + ret = -ESRCH; > + goto unlock; > + } > + > + ret = vm_insert_page(vma, addr, page); > + switch (ret) { > + case -EBUSY: > + /* > + * EBUSY is ok. Someone installed the pte first but the > + * lru_page->page_ptr has not been updated yet. Discard > + * our page and look up the one already installed. > + */ > + ret = 0; > + __free_page(page); > + npages = get_user_pages_remote(alloc->mm, addr, 1, 0, &page, NULL); This will trigger a page fault if we don't find what we expect (are races with e.g., MADV_DONTNEED possible?), is that really desired or not a problem? -- Cheers, David / dhildenb