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b=aTyHgKdQbCeZMl4qnEalSfONfzkg+pOWAJVo9pu//fpm5DvhUilKGpqE24MGZUWjz e8wxDLjsEt2LRRovfsWbp6+ueCLXRemNDU6ru5LyLo/RdmMYkehj0hdY/BfezN0SIR 6rXorPnoRbg0Gq6FTNKawXTYNP/YCIN+XKqwFxrqJX7TBPK+xsgnC8/CNv2AEYMna+ IWr1p90dtow6W/Zi6KWUYe/5p/IQxNtKZ+ys4kpDRpBKPU7GTg8+cvWjOZzISVxAgz 9gqz1fIOsSgPv5CPQan0og26oJfnPuQtRw2OFs282EWySnp6PYyV2TdjEAQH5EC+u/ yMkpHFF5r+KMg== Message-ID: <23623534-a163-4ffa-8538-b5aff7daecaf@kernel.org> Date: Tue, 20 Oct 2026 10:47:07 +0200 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] hugetlb: retry private VMA locking when unmapping folios To: Daehyeon Ko <4ncienth@gmail.com>, Muchun Song , Oscar Salvador Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261015170551.2656546-1-4ncienth@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+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: <20261015170551.2656546-1-4ncienth@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9604A1C0003 X-Stat-Signature: 9k6qffbt86d4rgt7nyqcraffpzdqos4g X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792486031-123167 X-HE-Meta: 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 2+OPwoRW EbPiSXOS/IR6fIHsVLi88viu6iblYZkLtz8/YtpkmxdEbsJaQJGZsyhZ4aRpMOxem7mo3qK2MaabZui5CaY/m54QvOOFf6LopUnUGClSwgaDrKv6PuIb5AezYa+W3alYTSNxSB3ln7gqPB6bXaYnfURnCT//g2NgZPb0P1QRO19ghPfWKuiKMl6YBnv5VdPQ//wV0nyyrD2Dyorp8YPG9DwhsiIJ/KtgUPbOnuifDLy/ZRe5uwFuJrbVTTFH4uCA+tR5eKpKG8DqVhJgA2KTh5R2NlBkNwoA2rU1JG1xtiDJSM2WirqOizceyuPLYod2WRTUMvjadBq0/+MGGG3QemZD+mqd0eUT70OCyEo/SZnDI0eA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/15/26 19:05, Daehyeon Ko wrote: > hugetlb_unmap_file_folio() takes a reference to the hugetlb_vma_lock in > vm_private_data when its VMA trylock fails. It then drops i_mmap_rwsem and > waits for the lock in the established order. > > That fallback is only valid for VM_MAYSHARE VMAs. Since commit > bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs"), the > trylock can also fail for a private owner VMA. Its vm_private_data contains > resv_map | HPAGE_RESV_OWNER, not a hugetlb_vma_lock. The fallback then > performs a misaligned refcount operation and treats reservation-map list > fields as an rwsem. > > Private reservation maps have no stable VMA backpointer. Drop i_mmap_rwsem > and restart the interval-tree walk when their trylock fails. Keep the > referenced fallback for shareable VMAs. > > On a system with a pre-provisioned hugepage pool, an unprivileged > reproducer racing mprotect() with hole punching triggered the refcount > warning followed by a general protection fault in rwsem_down_write_slowpath > on v7.3-rc5 and 6.12.111. With this change, a v7.3-rc5 KASAN+LOCKDEP build > completed 1,000 rounds and 64,000 hole punches without a warning, lockdep > report, oops, or panic. The reproducer is available privately on request. > > Fixes: bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> > --- > fs/hugetlbfs/inode.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index 7611a8470ea265..9a676228e2070a 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -402,6 +402,17 @@ static void hugetlb_unmap_file_folio(struct hstate *h, > continue; > > if (!hugetlb_vma_trylock_write(vma)) { > + /* > + * The referenced fallback below is specific to the > + * hugetlb_vma_lock stored by shareable VMAs. A private > + * owner VMA stores a tagged resv_map pointer here instead. > + */ > + if (!(vma->vm_flags & VM_MAYSHARE)) { > + i_mmap_unlock_write(mapping); > + cond_resched(); > + i_mmap_lock_write(mapping); > + goto retry; That looks like we can just live-lock now? > + } > vma_lock = vma->vm_private_data; This whole function is a mess. I have the following AI fix in a queue-of-fixes to go through and send out. The description is a bit mouthful, but the fix itself looks much cleaner (just skip the write-lock for VMAs that don't need it): Does that make sense? commit 12a35d8ee3e638129080c2bb13c0a35c873b5257 Author: Josef Bacik Date: Thu Oct 8 06:55:26 2026 +0000 hugetlbfs: fix unmapping a folio from a private vma hugetlb_unmap_file_folio() unmaps a folio which is about to leave the page cache from every vma that maps it. Where it can not get the lock of a vma with hugetlb_vma_trylock_write(), it takes vma->vm_private_data for a struct hugetlb_vma_lock, gets a reference to it, drops i_mmap_rwsem and sleeps on its rw_sema. Since commit bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") the trylock can fail for a MAP_PRIVATE vma that owns a reservation map, too. The lock of such a vma is resv_map->rw_sema, which every fault in the vma holds for reading, and its vm_private_data is the address of the resv_map with HPAGE_RESV_OWNER in bit 0. kref_get() and down_write() then work on the bytes of the resv_map, one byte off. A private vma maps a folio of the page cache after a read fault. Three threads of an unprivileged process are enough, on a hugetlb memfd: one reads a page through a private mapping, one writes to another page of that mapping, one allocates the first page with fallocate() and punches it out again. ftruncate() and MADV_REMOVE do as well as the hole punch. refcount_t: addition on 0; use-after-free. WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x6a/0x90 remove_inode_hugepages+0x49d/0x530 hugetlbfs_fallocate+0x4bf/0x5f0 vfs_fallocate+0x13d/0x330 On x86-64, saturating the "reference count" stores 0xc0 into the first byte of resv_map->lock: the next fault in the vma spins in region_chg() for ever. down_write() either takes a list pointer, shifted by one byte, for the owner and dies of a general protection fault, or spins with interrupts off on what it takes for the wait_lock, in both cases with the fault mutex and the inode lock held. Leave the lock of a vma that is not shareable alone, as it was before that commit. That lock keeps faults out of the vma until MADV_DONTNEED has freed its pages. It is not needed here: the caller holds the fault mutex of the index, so nobody can map the folio or replace it by a copy, and i_mmap_rwsem, held for writing, keeps the vma in the file's tree and its page tables in place. Fixes: bf4916922c60 ("hugetlbfs: extend hugetlb_vma_lock to private VMAs") Assisted-by: LLM Signed-off-by: Josef Bacik diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index d21dbcdc705ed..02cec281ceba5 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -401,6 +401,19 @@ static void hugetlb_unmap_file_folio(struct hstate *h, if (!hugetlb_vma_maps_pfn(vma, v_start, pfn)) continue; + /* + * Only a shareable vma has a struct hugetlb_vma_lock. The + * lock of a private vma lives in its resv_map and keeps + * faults away from MADV_DONTNEED; it is not needed here: + * the fault mutex holds off faults on this index, and + * i_mmap_rwsem everybody who zaps or frees page tables. + */ + if (!__vma_shareable_lock(vma)) { + unmap_hugepage_range(vma, v_start, v_end, NULL, + ZAP_FLAG_DROP_MARKER); + continue; + } + if (!hugetlb_vma_trylock_write(vma)) { vma_lock = vma->vm_private_data; /* -- Cheers, David