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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce57d3desm22829660f8f.7.2025.10.14.02.35.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Oct 2025 02:35:47 -0700 (PDT) Message-ID: Date: Tue, 14 Oct 2025 11:35:46 +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 v6] hugetlbfs: move lock assertions after early returns in huge_pmd_unshare() To: Deepanshu Kartikey , muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, broonie@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com References: <20251014050609.349461-1-kartikey406@gmail.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: <20251014050609.349461-1-kartikey406@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14.10.25 07:06, Deepanshu Kartikey wrote: > When hugetlb_vmdelete_list() processes VMAs during truncate operations, > it may encounter VMAs where huge_pmd_unshare() is called without the > required shareable lock. This triggers an assertion failure in > hugetlb_vma_assert_locked(). > > The previous fix in commit dd83609b8898 ("hugetlbfs: skip VMAs without > shareable locks in hugetlb_vmdelete_list") skipped entire VMAs without > shareable locks to avoid the assertion. However, this prevented pages > from being unmapped and freed, causing a regression in fallocate(PUNCH_HOLE) > operations where pages were not freed immediately, as reported by Mark Brown. > > A subsequent fix in commit 06e8ca1b3dca ("hugetlbfs: check for shareable > lock before calling huge_pmd_unshare()") addressed this by checking > __vma_shareable_lock() in the caller before calling huge_pmd_unshare(). > However, a cleaner approach is to move the lock assertions in > huge_pmd_unshare() itself to after the early return checks. The assertions > are only needed when actual PMD unsharing work will be performed. If the > function returns early because sz != PMD_SIZE or the PMD is not shared, > no locks are required. > > This patch removes the check added in commit 06e8ca1b3dca ("hugetlbfs: > check for shareable lock before calling huge_pmd_unshare()") and instead > moves the assertions inside huge_pmd_unshare(), keeping all the logic > within the function itself. > > Reported-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com > Reported-by: Mark Brown > Closes: https://syzkaller.appspot.com/bug?extid=f26d7c75c26ec19790e7 > Fixes: dd83609b8898 ("hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list") > Suggested-by: David Hildenbrand > Suggested-by: Oscar Salvador > Tested-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com > Link: https://lore.kernel.org/mm-commits/20250925203504.7BE02C4CEF7@smtp.kernel.org/ [v1] > Link: https://lore.kernel.org/mm-commits/20250928185232.BEDB6C4CEF0@smtp.kernel.org/ [v2] > Link: https://lore.kernel.org/linux-mm/20251003174553.3078839-1-kartikey406@gmail.com/ [v3] > Link: https://lore.kernel.org/linux-mm/20251008052759.469714-1-kartikey406@gmail.com/ [v4] > Link: https://lore.kernel.org/linux-mm/CADhLXY72yEVDjXWfxBUXfXhNfb8MWqwJmcb1daEHmDeFW+DRGw@mail.gmail.com/ [v5] > Signed-off-by: Deepanshu Kartikey > --- > Changes in v6: > - Remove __vma_shareable_lock() check from __unmap_hugepage_range() > that was added in v4 (commit 06e8ca1b3dca) > - Move lock assertions after early returns in huge_pmd_unshare() > - Complete implementation of David's cleaner approach > > Changes in v5: > - Incomplete: only moved assertions, forgot to remove v4 check > > Changes in v4: > - Check __vma_shareable_lock() in __unmap_hugepage_range() before calling > huge_pmd_unshare() per Oscar's suggestion > > Changes in v3: > - Add ZAP_FLAG_NO_UNSHARE to skip only PMD unsharing > > Changes in v2: > - Skip entire VMAs without shareable locks (caused PUNCH_HOLE regression) > > Changes in v1: > - Initial fix attempt > --- > mm/hugetlb.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 85b2dac79d25..0455119716ec 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5885,7 +5885,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, > } > > ptl = huge_pte_lock(h, mm, ptep); > - if (__vma_shareable_lock(vma) && huge_pmd_unshare(mm, vma, address, ptep)) { > + if (huge_pmd_unshare(mm, vma, address, ptep)) { > spin_unlock(ptl); > tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); > force_flush = true; > @@ -7614,13 +7614,12 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, > p4d_t *p4d = p4d_offset(pgd, addr); > pud_t *pud = pud_offset(p4d, addr); > > - i_mmap_assert_write_locked(vma->vm_file->f_mapping); > - hugetlb_vma_assert_locked(vma); > if (sz != PMD_SIZE) > return 0; > if (!ptdesc_pmd_is_shared(virt_to_ptdesc(ptep))) > return 0; > - > + i_mmap_assert_write_locked(vma->vm_file->f_mapping); > + hugetlb_vma_assert_locked(vma); > pud_clear(pud); > /* > * Once our caller drops the rmap lock, some other process might be Can you resend based on mm/mm-stable please? Looks like this one is based on v5. -- Cheers David / dhildenb