From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 115E3344030 for ; Fri, 17 Apr 2026 11:58:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776427087; cv=none; b=cwFP8DOsLJO/70LxICw+ctfXOd4zydTDHZ5dbXvbVQDqrJRcbAcNEs+PJju0q6eDu/2ebsNXhS6nq/YSU5iezKoahw53UmwK37apZDNNyUc4y1Dx2W+Z+7YGg8/RipEkt+dzpuVmmRhRvsAFnsYYzfRMu6RXx/gcBuB1K2yOwS0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776427087; c=relaxed/simple; bh=xhQnXncuO0tw+y17tTHOqzQNM1XVHhISnPz13HWA57g=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=aZsOmMa0q8Wq1LQjJI4zoO5mItSo87uie04ufuFKxsOWsP6fBcJwlmy4UC6dKEQ1L7R4rM5MeXjf/wU4J8nTVmLRbdMd6PBw398WOtHoYGj30tD2OtICJ7n7PC0k6BNFOeC166Doo0wcsqTey5KMx2tG1HEzlCq4L1Xl7P3adaM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XsD5zSOq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XsD5zSOq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C66FAC19425; Fri, 17 Apr 2026 11:58:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776427086; bh=xhQnXncuO0tw+y17tTHOqzQNM1XVHhISnPz13HWA57g=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; 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 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] 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 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