From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DDCEB3F327F for ; Wed, 5 Aug 2026 09:07:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785920844; cv=none; b=TtyKzLuY3BINuNQOr5ELhTrKo++TSH3e6rdf4KGm4S+aeNtg0X0dOiIxJun90rFylBciDePCUukn5EcYARQa8b5AAdbK0PRjAYVAYm1zamjf+nzY1GTKYupdWop3ALA+lmo6chMBTGM/4MisoIbW34tasdLeRadcR9M7GbhqECw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785920844; c=relaxed/simple; bh=KupNdHNfcQGrLNLHhhBOVqFjxKhhIIQj/Vocvo11CXE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fQ4Dhx6kGlgqxofqurs/ggvg1S8ixUqmCJ0ElhsTNmIKlDL7vPVWnWwUieHwTff+7kUtAhcZo/5pchiDLmskhL8NebgXUGIuhE/H3E6gbBi80J6gSRnYA3yfkWVfQs+691SrEdviKvdhFtIWUaKX3Nqtr00X6vMhrv/FfHLZvh8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iBdhs7jU; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iBdhs7jU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 536EF1F000E9; Wed, 5 Aug 2026 09:07:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785920842; bh=n6j+r2aySq3vbagzG6uXiIoHKnNOhVDFA/2TCxgRiS0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iBdhs7jUQaHuD4S0GiReJEJbIqkaUBKtt7iV461bZhDSVS24pXpFDQazjk6hUJNZU a3/vHMxqwTi6TSXMWvlmCKEaZpI+MDD+su2F6wyYH9BCDj9NUJcFnb+KElhOVS17Wg yQ8jUnmcYvQo4DuXxZmvEU0SYCsMDGdXIYxK2LUxrmQyVzqYvacOIlCb89UJNflFhb HQwNu6HU+f5lSVKhOu9/EhcPnDfyl+5nBXXQiMbRaO2prRQV8w5H2klhbHC5hGRsR3 jQkDNqRpfkZf7TVSTVW9uqIch8DCeFz4KRHDtf40QbQNHSiVC08Bjc4TnrwHsYPOMI JyykHZjJ2P86A== Message-ID: Date: Wed, 5 Aug 2026 11:07:18 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/memory-failure: fix concurrent access issue in min_order_for_split() To: dayou5941@163.com, akpm@linux-foundation.org, ljs@kernel.org Cc: ziy@nvidia.com, linux-mm@kvack.org, liyouhong , Sashiko , stable@vger.kernel.org References: <20260805072625.2437636-1-dayou5941@163.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/5/26 09:26, dayou5941@163.com wrote: > From: liyouhong > > min_order_for_split() accesses folio->mapping without proper > synchronization. While the compiler typically caches the value > in a register making a NULL deref unlikely in practice, the > real issue is that the callers in memory-failure.c do not hold > the folio lock at the time of the call: > > - memory_failure() explicitly drops the folio lock before calling > min_order_for_split(). > - soft_offline_in_use_page() has not yet acquired the folio lock > when calling min_order_for_split(). > > This means the value of folio->mapping may be modified by a > truncate or invalidate operation while min_order_for_split() is > executing, leading to a torn read or use of a stale mapping value. I recall that a mapping can get freed after truncating the last folio. But Lorenzo had some cocnerns about the validity of the report, so I'll let him reply. > > Fixes: 689b8986776c ("mm/memory-failure: improve large block size folio handling") > Reported-by: Sashiko > Closes: https://sashiko.dev/#/patchset/20260803060001.800638-1-dayou5941@163.com > Cc: stable@vger.kernel.org > Signed-off-by: liyouhong > --- > v2: > - Dropped the approach of caching folio->mapping inside min_order_for_split() in favor of adding the folio lock at the callers. > - Added VM_WARN_ON_ONCE_FOLIO() in min_order_for_split(). > - Updated the commit message to clarify that the real issue is the callers not holding the folio lock, rather than a TOCTOU race. > v1: https://lore.kernel.org/all/20260804035828.2684059-1-dayou5941@163.com/ > > --- > mm/huge_memory.c | 2 ++ > mm/memory-failure.c | 12 ++++++++++-- > 2 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 58cabe6af33d..e3f16dadc1d4 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -4300,6 +4300,8 @@ int folio_split(struct folio *folio, unsigned int new_order, > */ > unsigned int min_order_for_split(struct folio *folio) > { > + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); > + > if (folio_test_anon(folio)) > return 0; > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 3b1e6946821b..7391524b5046 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -2437,12 +2437,17 @@ int memory_failure(unsigned long pfn, int flags) > res = -EOPNOTSUPP; > goto unlock_mutex; > } > + > folio_unlock(folio); > > if (folio_test_large(folio)) { > - const int new_order = min_order_for_split(folio); > + const int new_order; > int err; > > + folio_lock(folio); > + new_order = min_order_for_split(folio); > + folio_unlock(folio); > + > /* > * The flag must be set after the refcount is bumped > * otherwise it may race with THP split. > @@ -2796,8 +2801,11 @@ static int soft_offline_in_use_page(struct page *page) > }; > > if (!huge && folio_test_large(folio)) { > - const int new_order = min_order_for_split(folio); > + const int new_order; > > + folio_lock(folio); > + new_order = min_order_for_split(folio); > + folio_unlock(folio); > /* > * If new_order (target split order) is not 0, do not split the > * folio at all to retain the still accessible large folio. We already grab the page lock in try_to_split_thp_page(). I think these needs a serious cleanup. While at it, we can fix the missing put_page() in case new_order != 0 in soft_offline_in_use_page() ... So i think we really should do the following: >From 58c4ccbb04e13c4c14ef7a94f4b44f8901183081 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Wed, 5 Aug 2026 11:01:46 +0200 Subject: [PATCH] tmp Signed-off-by: David Hildenbrand (Arm) --- mm/memory-failure.c | 46 +++++++++++++++------------------------------ 1 file changed, 15 insertions(+), 31 deletions(-) diff --git a/mm/memory-failure.c b/mm/memory-failure.c index aaf14608b30e2..de97a7a36764d 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1705,26 +1705,6 @@ static int identify_page_state(unsigned long pfn, struct page *p, return page_action(ps, p, pfn); } -/* - * When 'release' is 'false', it means that if thp split has failed, - * there is still more to do, hence the page refcount we took earlier - * is still needed. - */ -static int try_to_split_thp_page(struct page *page, unsigned int new_order, - bool release) -{ - int ret; - - lock_page(page); - ret = split_huge_page_to_order(page, new_order); - unlock_page(page); - - if (ret && release) - put_page(page); - - return ret; -} - static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn, struct address_space *mapping, pgoff_t index, int flags) { @@ -2509,7 +2489,6 @@ int memory_failure(unsigned long pfn, int flags) folio_unlock(folio); if (folio_test_large(folio)) { - const int new_order = min_order_for_split(folio); int err; /* @@ -2526,24 +2505,24 @@ int memory_failure(unsigned long pfn, int flags) * page is a valid handlable page. */ folio_set_has_hwpoisoned(folio); - err = try_to_split_thp_page(p, new_order, /* release= */ false); + + lock_page(p); + err = split_huge_page_to_order(p, min_order_for_split(folio)); + unlock_page(p); /* * If splitting a folio to order-0 fails, kill the process. * Split the folio regardless to minimize unusable pages. * Because the memory failure code cannot handle large * folios, this split is always treated as if it failed. */ - if (err || new_order) { - /* get folio again in case the original one is split */ - folio = page_folio(p); + folio = page_folio(p); + if (folio_test_large(folio)) { res = -EHWPOISON; kill_procs_now(p, pfn, flags, folio); put_page(p); action_result(pfn, MF_MSG_UNSPLIT_THP, MF_FAILED); goto unlock_mutex; } - VM_BUG_ON_PAGE(!page_count(p), p); - folio = page_folio(p); } /* @@ -2862,8 +2841,7 @@ static int soft_offline_in_use_page(struct page *page) }; if (!huge && folio_test_large(folio)) { - const int new_order = min_order_for_split(folio); - + lock_page(page); /* * If new_order (target split order) is not 0, do not split the * folio at all to retain the still accessible large folio. @@ -2871,8 +2849,14 @@ static int soft_offline_in_use_page(struct page *page) * preferred, split it to non-zero new_order like it is done in * memory_failure(). */ - if (new_order || try_to_split_thp_page(page, /* new_order= */ 0, - /* release= */ true)) { + if (!min_order_for_split(folio)) + ret = split_huge_page_to_order(page, 0); + else + ret = -EBUSY; + unlock_page(page); + + if (ret) { + put_page(page); pr_info("%#lx: thp split failed\n", pfn); return -EBUSY; } -- 2.43.0 Likely some more cleanups on top are possible. -- Cheers, David