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b=XsD5zSOqyCFf945CFny0tBQPXjvuOOwLUlQANOvR9JiZ1ZodUnC6TwwglTUdDw4jI MDe8p6m5H0OOy6wgJT+gXOkUoIEAToZlupdkQWmbsw1FMs+c/CQiYumN17Gvtd0ue5 8mGicZBvz+yT5Esgj1Vu/Aa/ON5ZUNtlPxP1T/uFqfzEjiLpgsByREuMKGVS17Td1c 2k2XndXz+79agXCdO+lRA4ZKlF+AQU3N63F8BDfZ0RS4xtX7nS58Ik2Itp8XJG4iiJ OAuwavCdgHOYPaoY3ABy616K2IO21dK646ae8gKfPT7GaeVRP62dQHaWnB0im0iZEg FfliC+RhoEEQw== Message-ID: Date: Fri, 17 Apr 2026 13:57:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: prepare anon_vma before swapin rmap From: "David Hildenbrand (Arm)" To: ZhengYuan Huang , akpm@linux-foundation.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, r33s3n6@gmail.com, zzzccc427@gmail.com References: <20260417011606.1089985-1-gality369@gmail.com> <66f67e51-819b-4c60-9f61-170db32362a2@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C737540009 X-Rspamd-Server: rspam12 X-Stat-Signature: hy8o5icbdahdoqzky5fmhmnuwt6qs9hm X-Rspam-User: X-HE-Tag: 1776427087-69645 X-HE-Meta: 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 5sM2ndvb sXCAPIXyE38Xist01YdrnfiK8uJgdCYe9PDu594GRSLXQxwAous+YmhUWeuvO1k6SXChxohmqik53zGRY/LxKk/P8pIgwY5MY2UlVVExWX7RFHpxXYtnGJxJu9lnlKlfdP0a7sPGzR32rEhsQ/hk5K7cZbmoJcVZga2pZNjoBbQEFaz7wnoqToYn1SxOJSjoIbwjwS1T/6I4pIFAvekqynQe9yHaMY1VYt6M6q+NgIv+iDAA1Nr47SxLchS94WWgqOotnu8wPc0cGZQK4QN2LeQcGz/gGAqawhFRa0FQNX1zGh6TEOGTDlCo/AOHsP1lzarRVZZPC5OZ0xxq6yb81fTyNUl6zk3DVzBda Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/17/26 12:53, David Hildenbrand (Arm) wrote: > On 4/17/26 03:16, ZhengYuan Huang wrote: >> [BUG] >> madvise(MADV_HWPOISON) can fault a swap entry back in through >> get_user_pages_fast() and hit: >> >> kernel BUG at mm/rmap.c:1364! >> Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI >> RIP: 0010:__folio_set_anon mm/rmap.c:1364 [inline] >> RIP: 0010:folio_add_new_anon_rmap+0x41d/0xc10 mm/rmap.c:1553 >> Call Trace: >> do_swap_page+0x14c5/0x5c30 mm/memory.c:4963 >> handle_pte_fault mm/memory.c:6198 [inline] >> __handle_mm_fault+0x1512/0x22f0 mm/memory.c:6336 >> handle_mm_fault+0x42f/0x820 mm/memory.c:6505 >> faultin_page mm/gup.c:1126 [inline] >> __get_user_pages+0x4b3/0x3400 mm/gup.c:1428 >> __get_user_pages_locked mm/gup.c:1692 [inline] >> __gup_longterm_locked+0x945/0x14b0 mm/gup.c:2476 >> gup_fast_fallback+0x8a3/0x2440 mm/gup.c:3220 >> get_user_pages_fast+0x64/0xb0 mm/gup.c:3298 >> madvise_inject_error mm/madvise.c:1456 [inline] >> madvise_do_behavior+0x503/0x860 mm/madvise.c:1875 >> do_madvise+0x17e/0x210 mm/madvise.c:1978 >> __do_sys_madvise mm/madvise.c:1987 [inline] >> __se_sys_madvise mm/madvise.c:1985 [inline] >> __x64_sys_madvise+0xae/0x120 mm/madvise.c:1985 >> ... >> >> [CAUSE] >> Commit a373baed5a9d ("mm: delay the check for a NULL anon_vma") moved >> anon_vma preparation out of the generic fault path and into the fault >> handlers that actually need to install anonymous rmap state. >> >> do_swap_page() was left behind. It can still restore anonymous mappings >> via folio_add_new_anon_rmap() or folio_add_anon_rmap_ptes(), but it does >> not call vmf_anon_prepare() first. On a VMA-lock fault this can leave >> vma->anon_vma NULL all the way down to __folio_set_anon(), which BUG_ONs >> on that violated invariant. >> >> [FIX] >> Prepare the faulting VMA's anon_vma once do_swap_page() has confirmed it >> is handling a real swap entry, before any swapin path can install >> anonymous rmap state. >> >> vmf_anon_prepare() already handles the retry rules for VMA-lock faults, >> and when anon_vma is already present this stays a single likely branch in >> the swap fault hot path. >> >> Fixes: a373baed5a9d ("mm: delay the check for a NULL anon_vma") >> Signed-off-by: ZhengYuan Huang >> --- >> I can reproduce this issue deterministically on v6.18, but I have not >> been able to reproduce it with the same setup on next-20260415. >> >> However, I have not identified a change that clearly explains the >> difference. From code inspection, do_swap_page() still appears able to >> reach folio_add_new_anon_rmap()/folio_add_anon_rmap_ptes() without a >> prior vmf_anon_prepare() > > > If there is an anon page swapped out, certainly at the allocation time > of that anon folio, there would have to be a anon_rmap allocated. > > During fork, the anon_rmap would have to be created as well. > > Something is off here. > Just speculating, we had commit 3b617fd3d317bf9dd7e2c233e56eafef05734c9d Author: Lorenzo Stoakes Date: Mon Jan 5 20:11:49 2026 +0000 mm/vma: enforce VMA fork limit on unfaulted,faulted mremap merge too Go into v6.19. Maybe there was a scenario where we could have lost vma->anon_vma during a merge, resulting in a swapped page in an anon_vma. If this cannot be reproduced on 6.19+,there is nothing to worry about. -- Cheers, David