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(p200300d82f42b000db8b7655f60f812b.dip0.t-ipconnect.de. [2003:d8:2f42:b000:db8b:7655:f60f:812b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e0156b0a8sm19931135e9.3.2025.09.11.02.31.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Sep 2025 02:31:04 -0700 (PDT) Message-ID: Date: Thu, 11 Sep 2025 11:31:03 +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 v1 6/9] mm: Change dup_mmap() recovery To: "Liam R. Howlett" , Andrew Morton Cc: maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , Charan Teja Kalla , shikemeng@huaweicloud.com, kasong@tencent.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, chrisl@kernel.org, Matthew Wilcox References: <20250909190945.1030905-1-Liam.Howlett@oracle.com> <20250909190945.1030905-7-Liam.Howlett@oracle.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250909190945.1030905-7-Liam.Howlett@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 09.09.25 21:09, Liam R. Howlett wrote: > When the dup_mmap() fails during the vma duplication or setup, don't > write the XA_ZERO entry in the vma tree. Instead, destroy the tree and > free the new resources, leaving an empty vma tree. > > Using XA_ZERO introduced races where the vma could be found between > dup_mmap() dropping all locks and exit_mmap() taking the locks. The > race can occur because the mm can be reached through the other trees > via successfully copied vmas and other methods such as the swapoff code. > > XA_ZERO was marking the location to stop vma removal and pagetable > freeing. The newly created arguments to the unmap_vmas() and > free_pgtables() serve this function. > > Replacing the XA_ZERO entry use with the new argument list also means > the checks for xa_is_zero() are no longer necessary so these are also > removed. > > Signed-off-by: Liam R. Howlett > --- > mm/memory.c | 6 +----- > mm/mmap.c | 42 +++++++++++++++++++++++++++++++----------- > 2 files changed, 32 insertions(+), 16 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 24716b3713f66..829cd94950182 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -408,8 +408,6 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas, > * be 0. This will underflow and is okay. > */ > next = mas_find(mas, tree_max - 1); > - if (unlikely(xa_is_zero(next))) > - next = NULL; > > /* > * Hide vma from rmap and truncate_pagecache before freeing > @@ -428,8 +426,6 @@ void free_pgtables(struct mmu_gather *tlb, struct ma_state *mas, > while (next && next->vm_start <= vma->vm_end + PMD_SIZE) { > vma = next; > next = mas_find(mas, tree_max - 1); > - if (unlikely(xa_is_zero(next))) > - next = NULL; > if (mm_wr_locked) > vma_start_write(vma); > unlink_anon_vmas(vma); > @@ -2129,7 +2125,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas, > mm_wr_locked); > hugetlb_zap_end(vma, &details); > vma = mas_find(mas, tree_end - 1); > - } while (vma && likely(!xa_is_zero(vma))); > + } while (vma); > mmu_notifier_invalidate_range_end(&range); > } > > diff --git a/mm/mmap.c b/mm/mmap.c > index 0f4808f135fe6..aa4770b8d7f1e 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1288,7 +1288,7 @@ void exit_mmap(struct mm_struct *mm) > arch_exit_mmap(mm); > > vma = vma_next(&vmi); > - if (!vma || unlikely(xa_is_zero(vma))) { > + if (!vma) { > /* Can happen if dup_mmap() received an OOM */ > mmap_read_unlock(mm); > mmap_write_lock(mm); > @@ -1858,20 +1858,40 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm) > ksm_fork(mm, oldmm); > khugepaged_fork(mm, oldmm); > } else { > + unsigned long max; > > /* > - * The entire maple tree has already been duplicated. If the > - * mmap duplication fails, mark the failure point with > - * XA_ZERO_ENTRY. In exit_mmap(), if this marker is encountered, > - * stop releasing VMAs that have not been duplicated after this > - * point. > + * The entire maple tree has already been duplicated, but > + * replacing the vmas failed at mpnt (which could be NULL if > + * all were allocated but the last vma was not fully set up). > + * Use the start address of the failure point to clean up the > + * partially initialized tree. > */ > - if (mpnt) { > - mas_set_range(&vmi.mas, mpnt->vm_start, mpnt->vm_end - 1); > - mas_store(&vmi.mas, XA_ZERO_ENTRY); > - /* Avoid OOM iterating a broken tree */ > - mm_flags_set(MMF_OOM_SKIP, mm); > + if (!mm->map_count) { > + /* zero vmas were written to the new tree. */ > + max = 0; > + } else if (mpnt) { > + /* partial tree failure */ > + max = mpnt->vm_start; > + } else { > + /* All vmas were written to the new tree */ > + max = ULONG_MAX; > } > + > + /* Hide mm from oom killer because the memory is being freed */ > + mm_flags_set(MMF_OOM_SKIP, mm); > + if (max) { > + vma_iter_set(&vmi, 0); > + tmp = vma_next(&vmi); > + flush_cache_mm(mm); > + unmap_region(&vmi.mas, /* vma = */ tmp, > + /*vma_min = */ 0, /* vma_max = */ max, > + /* pg_max = */ max, /* prev = */ NULL, > + /* next = */ NULL); > + charge = tear_down_vmas(mm, &vmi, tmp, max); > + vm_unacct_memory(charge); > + } > + __mt_destroy(&mm->mm_mt); Usually comment about just calling things start/end, maybe with prefix if required. Apart from that, LGTM. -- Cheers David / dhildenb