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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4535fdf82f9sm171243685e9.29.2025.06.24.06.58.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Jun 2025 06:58:42 -0700 (PDT) Message-ID: Date: Tue, 24 Jun 2025 15:58:41 +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 v2 1/4] mm, madvise: simplify anon_name handling To: Vlastimil Babka , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Colin Cross Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250624-anon_name_cleanup-v2-0-600075462a11@suse.cz> <20250624-anon_name_cleanup-v2-1-600075462a11@suse.cz> 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: <20250624-anon_name_cleanup-v2-1-600075462a11@suse.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 24.06.25 15:03, Vlastimil Babka wrote: > Since the introduction in 9a10064f5625 ("mm: add a field to store names > for private anonymous memory") the code to set anon_name on a vma has > been using madvise_update_vma() to call replace_anon_vma_name(). Since > the former is called also by a number of other madvise behaviours that > do not set a new anon_name, they have been passing the existing > anon_name of the vma to make replace_vma_anon_name() a no-op. > > This is rather wasteful as it needs anon_vma_name_eq() to determine the > no-op situations, and checks for when replace_vma_anon_name() is allowed > (the vma is anon/shmem) duplicate the checks already done earlier in > madvise_vma_behavior(). It has also lead to commit 942341dcc574 ("mm: > fix use-after-free when anon vma name is used after vma is freed") > adding anon_name refcount get/put operations exactly to the cases that > actually do not change anon_name - just so the replace_vma_anon_name() > can keep safely determining it has nothing to do. > > The recent madvise cleanups made this suboptimal handling very obvious, > but happily also allow for an easy fix. madvise_update_vma() now has the > complete information whether it's been called to set a new anon_name, so > stop passing it the existing vma's name and doing the refcount get/put > in its only caller madvise_vma_behavior(). > > In madvise_update_vma() itself, limit calling of replace_anon_vma_name() > only to cases where we are setting a new name, otherwise we know it's a > no-op. We can rely solely on the __MADV_SET_ANON_VMA_NAME behaviour and > can remove the duplicate checks for vma being anon/shmem that were done > already in madvise_vma_behavior(). > > Additionally, by using vma_modify_flags() when not modifying the > anon_name, avoid explicitly passing the existing vma's anon_name and > storing a pointer to it in struct madv_behavior or a local variable. > This prevents the danger of accessing a freed anon_name after vma > merging, previously fixed by commit 942341dcc574. > > Signed-off-by: Vlastimil Babka > --- > mm/madvise.c | 37 +++++++++++++------------------------ > 1 file changed, 13 insertions(+), 24 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 4491bf080f55d6d1aeffb2ff0b8fdd28904af950..fca0e9b3e844ad766e83ac04cc0d7f4099c74005 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -176,25 +176,29 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, > } > #endif /* CONFIG_ANON_VMA_NAME */ > /* > - * Update the vm_flags on region of a vma, splitting it or merging it as > - * necessary. Must be called with mmap_lock held for writing; > - * Caller should ensure anon_name stability by raising its refcount even when > - * anon_name belongs to a valid vma because this function might free that vma. > + * Update the vm_flags and/or anon_name on region of a vma, splitting it or > + * merging it as necessary. Must be called with mmap_lock held for writing. > */ > static int madvise_update_vma(vm_flags_t new_flags, > struct madvise_behavior *madv_behavior) > { > - int error; > struct vm_area_struct *vma = madv_behavior->vma; > struct madvise_behavior_range *range = &madv_behavior->range; > struct anon_vma_name *anon_name = madv_behavior->anon_name; > + bool set_new_anon_name = madv_behavior->behavior == __MADV_SET_ANON_VMA_NAME; > VMA_ITERATOR(vmi, madv_behavior->mm, range->start); > > - if (new_flags == vma->vm_flags && anon_vma_name_eq(anon_vma_name(vma), anon_name)) > + if (new_flags == vma->vm_flags && (!set_new_anon_name || > + anon_vma_name_eq(anon_vma_name(vma), anon_name))) > return 0; > > - vma = vma_modify_flags_name(&vmi, madv_behavior->prev, vma, > + if (set_new_anon_name) > + vma = vma_modify_flags_name(&vmi, madv_behavior->prev, vma, > range->start, range->end, new_flags, anon_name); > + else > + vma = vma_modify_flags(&vmi, madv_behavior->prev, vma, > + range->start, range->end, new_flags); > + > if (IS_ERR(vma)) > return PTR_ERR(vma); > > @@ -203,11 +207,8 @@ static int madvise_update_vma(vm_flags_t new_flags, > /* vm_flags is protected by the mmap_lock held in write mode. */ > vma_start_write(vma); > vm_flags_reset(vma, new_flags); > - if (!vma->vm_file || vma_is_anon_shmem(vma)) { > - error = replace_anon_vma_name(vma, anon_name); > - if (error) > - return error; > - } > + if (set_new_anon_name) > + return replace_anon_vma_name(vma, anon_name); Took me a second to find where this is already checked (-> madvise_vma_behavior()). :) Acked-by: David Hildenbrand -- Cheers, David / dhildenb