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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 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; 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: <20260805072625.2437636-1-dayou5941@163.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 6okrad5r4sjah1j8ob6bmqjuh4ss3mhb X-Rspamd-Queue-Id: 8340718000C X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1785920843-990940 X-HE-Meta: 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 7xtBxPW9 iBnzOSJQOV/oU5jbO7UAYAHYK0Ol27NKZa/FaGh/HcNhWtHdWBvMWZI1Tg8ID5RtwS1MCxQ0ydutYxulxrxIwUh4Em41VIqD6siyWRmkPJzIfUEtBURnSTSQuXCimCJIijyNBvKbDh54+ohiYXC7unWH0fZnLBRzzOWZuEgGkw9HuFgENUEdZsS2Yx59zD+DzW7BAnFHyAxGfltZqY5/PuVC4mIdnxJi0P4Z4fnYpm1kdha7Co1fKbiYZlzBEKTAk9doenlAphK4gFINVhfb0MxB+mwS4UmjqN+Upww8O92RIIXgqerqCaUGeVzjIveSANo48IUeyn+kJsTfHciyzZuVyyG3ybls9gSaGI+HqTsePJUZuGnecGvJMVmyYxySSEtSzZ7f1lNOVPbxqOnuBx5bbWj/GyViGoRx+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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