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 7DB2638E8BF; Tue, 14 Jul 2026 13:01:51 +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=1784034112; cv=none; b=kY0Ryw8uP9hQALwHnINm16kAG6hlwiYO8y0/2G9jWukFaFpZI/By6kNNdFXlHxcGFii1R4cptDDE5KZaFZcuJL5TV+rBjbEufFPLXzJ1fX8cQ7D4DvR5RnYea3W1ooprqCYE3cKw2Ufyrx2mgeYwltDd8v9sg/IML0SSi6jnyC0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784034112; c=relaxed/simple; bh=GLMaWwLOh/ycz857H6uubMqc9SqgwrtKJG1YSD6ft38=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EnWJ3PaEu/bFylOx5HAUHMGj750BHa10p6Z2bpXzgMmXOGxbWOF89GRE/jwrYOg5zGbhEDvcgrAjtznuP1+ZwpO0banMwJr4KjVtG4IQjp4g5mNS/aEQr4QWtEklMrNl1+alyma/CSWyIT/HcY5aKms7q397GiRxay+ST9+gppQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=k5c7YCIU; 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="k5c7YCIU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD4B71F000E9; Tue, 14 Jul 2026 13:01:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784034111; bh=HuK4P6aqO8DESV6CHxhF1gUmZk/0pbyK+8uhsekdIXE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=k5c7YCIU9HDxHlg4W4qOo0RvYVF1Yi9F2s+I6qWTMFhO7y5LTv3AAIisV2EWRK7gt G71ZbZF4BS24Cc39/TUyfVc5uhFkyz1eBRQWXthjI6/20woS6JR6HyEDDmL6x8i/2F DcSgKfv3TmJNEK5wNp/jycuq4f8CVqmXXBJZZun553j3NwhJj4KAGuhBwn1OmnwVy4 VuiGlTDHXX0ZSUBi3SsBZzNo3DQL4esXhTMzEzjfqW0tCG7qN+LvbgwN6KHFDf9WHQ h/sVeewLC8mS4d+YQIElGTCBmyQUMpOqmwK0Yw7f5mOPS1Udc2KNg1QbwGQlpNOdHu 5iV3J2HxCieBg== Message-ID: Date: Tue, 14 Jul 2026 15:01:46 +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 v2 1/5] mm/memory-failure: keep the folio, not the poisoned subpage, locked across split To: Kiryl Shutsemau , Andrew Morton , Lorenzo Stoakes , Miaohe Lin , Naoya Horiguchi Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Hao Zhang , Hao Zhang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kiryl Shutsemau (Meta)" , stable@vger.kernel.org References: <20260714122344.351895-1-kirill@shutemov.name> <20260714122344.351895-2-kirill@shutemov.name> 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: <20260714122344.351895-2-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/14/26 14:23, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > try_to_split_thp_page() locked the poisoned page and passed it to > split_huge_page_to_order(), which returns that very page locked to the > caller. For a tail page that means __folio_split() runs with @lock_at > pointing into the middle of the folio. > > __folio_split() dereferences the mapping after the split completes > (shmem_uncharge(), i_mmap_unlock_read()). The only thing keeping the > inode alive across that is the locked @lock_at folio: while it stays in > the page cache, eviction cannot complete. > > But a tail @lock_at can lie beyond EOF -- e.g. part of a shmem THP that > reaches past i_size while the file is being truncated. The split then > drops it from the page cache yet still returns it locked, so the pin is > gone and a racing final iput() can evict and RCU-free the inode while > __folio_split() is still running: > > BUG: KASAN: slab-use-after-free in __up_read+0x634/0x790 > i_mmap_unlock_read include/linux/fs.h:537 [inline] > __folio_split+0x732/0x1640 mm/huge_memory.c:4100 > try_to_split_thp_page+0xab/0x390 mm/memory-failure.c:1675 > memory_failure+0x1394/0x26e0 mm/memory-failure.c:2470 > > Freed by task 4601: > shmem_free_in_core_inode+0x54/0xb0 mm/shmem.c:5177 > evict+0x57f/0xac0 fs/inode.c:870 > > Split the folio as a folio, via split_folio_to_order(), so the head is > the anchor left locked. The head is piece 0, which the beyond-EOF drop > loop never removes (it starts at folio_next(folio)), so the split always > leaves it in the page cache and the inode stays pinned for the whole of > __folio_split(). memory_failure() and soft offline re-lock the poisoned > subpage's folio themselves after the split, so they do not depend on it > being returned locked. > > Reported-by: Hao Zhang > Closes: https://lore.kernel.org/linux-mm/20260710071344.GA106129@zh-pc > Fixes: baa355fd3314 ("thp: file pages support for split_huge_page()") > Cc: > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/memory-failure.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 51508a55c405..68d42cbed458 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -1657,11 +1657,18 @@ static int identify_page_state(unsigned long pfn, struct page *p, > static int try_to_split_thp_page(struct page *page, unsigned int new_order, > bool release) > { > + struct folio *folio = page_folio(page); > int ret; > > - lock_page(page); > - ret = split_huge_page_to_order(page, new_order); > - unlock_page(page); > + /* > + * Lock and split at the head, not the poisoned subpage: __folio_split() > + * keeps the anchor folio locked and needs it to stay in the page cache > + * to pin the inode. A tail beyond EOF would be dropped yet returned > + * locked, losing that pin. The caller re-locks @page afterwards. > + */ > + folio_lock(folio); > + ret = split_folio_to_order(folio, new_order); > + folio_unlock(folio); With a non-uniform split it would actually make a difference: we'd want to split such that we the other folio pages minimal. split_folio_to_order() always seems to end up in __split_huge_page_to_list_to_order() where we do a SPLIT_TYPE_UNIFORM. I recall discussing with Zi and Willy that in the future we'd want to convert more places to do a non-uniform split. So I'm afraid that would just re-introduce the problem then. -- Cheers, David