From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E6529606A324 for ; Wed, 28 Oct 2026 21:45:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=UmI/Cm2S Received: by kanga.kvack.org (Postfix) id 0D30E6B00EF; Wed, 28 Oct 2026 17:45:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0836C6B05B1; Wed, 28 Oct 2026 17:45:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E8DDE6B05B2; Wed, 28 Oct 2026 17:45:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id BC1126B00EF for ; Wed, 28 Oct 2026 17:45:56 -0400 (EDT) Received: from smtpin06.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 4B615401B2 for ; Wed, 28 Oct 2026 21:45:56 +0000 (UTC) X-FDA: 85373367912.06.0B8C2EE Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf31.hostedemail.com (Postfix) with ESMTP id 3908320003 for ; Wed, 28 Oct 2026 21:45:55 +0000 (UTC) Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="UmI/Cm2S"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793223954; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=fbrRyxoimymYWhLJDCrGjtIVJ2fCjNVZxRXAPG71cWM=; b=Zf8YCkhrd0X+RzxNKJvwRiyILLpH0M0dz8yVK1hAMaLG/wUMseGtMGraTklGe0mI5iLq1M PpwkFx1963TNJYeZOTrU9UlExM07HB3tEQKXNxzXY6nDGFInjJofiUj8P1vypp+8vYzKT1 tvOO0NFFb/MP1I5JP4DCbqawjDKDhco= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="UmI/Cm2S"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793223954; b=SMmH9rvsI0mIwEtxPCIWPJADgZxDQXZ1RNcMnsGgSRSCWWJmScaTqO/zsEA+E1tK7wEIUe hPKA2DvX1znP+2TvX2IbAqhK+zxE2uGFq2mOEua25gMEpAlnTBhImagKjbzeGp+XiFTpvM 43Zoe7zRZHcvUrLoGz/xUsKFpxHWMNo= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 76A5840E1B; Wed, 28 Oct 2026 21:45:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FAFF1F01825; Wed, 28 Oct 2026 21:45:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793223953; bh=fbrRyxoimymYWhLJDCrGjtIVJ2fCjNVZxRXAPG71cWM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=UmI/Cm2SrjBwj1BQYLo3s5sb7BMvx3t0fFbpR+mnITEWqKp5wlIiQPLln6BkXC9rt m6RZcvbkbKhA9qmDG4og48sVDa+PZnbyZkQMFjd/pOyk7PvFVJGwxKxmmGk3y4VKPW r2JDXQHZuX8Fv0WEovG6xsUoSWzKG1qoZx3iP1IdmN4kwUKF7gtBwhyTc6yUCKAP9Z tncWISQ22ZSz7AEGqiuFHP15FaJB7aOWP6s0aM9o3U08JKSaV3w1w5r5Gyr1Sq97Fu XkskqqkTDrcPRQNfM87sfV+bHscqsB/Uf8B1Ourx7X22qLn5cpDzeSEB1WAvR51lNH luun1fqwX46mg== Message-ID: <2f2ef336-2186-4f20-b7f5-565e60471bda@kernel.org> Date: Wed, 28 Oct 2026 22:45:34 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 05/46] mm/truncate: look again if a folio left the mapping To: Kiryl Shutsemau Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-5-6f74bec9a5bb@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 3908320003 X-Rspam-User: X-Stat-Signature: unng8ie6uin3txfz6reti9jbrfag1hqu X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1793223955-639899 X-HE-Meta: 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 vqbjnWx8 bThDhPyeHyBVpUvr3FEHNhchnhFEYRfXCZWgHCLhqJrchfNupl5QOZWMmc/Qij5FLuQcUurt0NED2nU+Wf0E3Jy9lXzov9KJzQQvQmREiEG2UOPQLFbswVVW+bK3n8vQLmzB/2aXoYMeM4Z3QbEzA0xmfykf2jQv2M1BGDwW1vQ2vasn1WqW/8n0LhLCuEbBwnYjGrxPyL/szqXb454GGsbKTAyn9ZlW6szElbyPSoWFC/++6TxZIMqXTcX4md3x5rFC8+jFCrDe8MixcZrJYYkEOyq+3NZ725g+B1lYwY/y1f8DrPBv7i+Dl32UMwMMbuDhrkZT266DP+K93HfH3lVRT+Lm+S5uVxSakmRqcSQp40SC2TW1TgC7EexOs+pGtnUmPkftVFMCBzQBT8Bm1TfbWbFhTU5WcHN1jOKsQLNlvhVZLttirfZL8bJREdQ544lIE Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/28/26 17:54, Kiryl Shutsemau wrote: > On Tue, Oct 27, 2026 at 12:17:25AM +0100, David Hildenbrand (Arm) wrote: >> invalidate_inode_pages2_range() skips a folio which no longer belongs to >> the mapping by the time it has got the folio lock, on the assumption >> that somebody else has removed it from the page cache. But the folio may >> have been replaced, and then there is a new folio with the same data at >> that index. >> >> For most cases, like folio migration, that is impossible. However, >> collapse_file() only checks the refcount of the old folios, under the >> i_pages lock, and relies on their folio locks from there on. That works for >> users which repeat the lookup when they find folio->mapping changed. >> The following scenario is, however, possible: >> >> CPU0 pwrite(O_DIRECT) CPU1 collapse_file() >> kiocb_invalidate_pages() >> read the folio (old data), lock it >> refcount check >> the write completes copy to new_folio >> kiocb_invalidate_post_direct_write() >> find_get_entries() -> old folio >> folio_lock() ... xas_store(new_folio) >> folio->mapping = NULL >> folio_unlock(folio) >> folio->mapping != mapping >> -> continue > > The diagram reads as if the folio lock should have closed the race. It > might be clearer with CPU0's folio_lock() after CPU1's folio_unlock(), > since the reference taken after the refcount check is what matters: I'll use that, thanks! > > CPU0 pwrite(O_DIRECT) CPU1 collapse_file() > kiocb_invalidate_pages() > read the folio (old data), lock it > refcount check > the write completes copy to new_folio > kiocb_invalidate_post_direct_write() > find_get_entries() -> old folio > xas_store(new_folio) > folio->mapping = NULL > folio_unlock(folio) > folio_lock() > folio->mapping != mapping > -> continue > >> In that scenario, the collapsed folio with the data from before the write >> stays in the page cache after the write has returned. >> >> This used to be impossible, as khugepaged only collapsed files that nobody >> had open for writing. >> >> Restart the lookup at that index, like shmem_undo_range() does. The same >> problem seems to exist in truncate_inode_pages_range() as well when >> truncate_inode_folio() fails, so handle it there as well. >> >> Fixes: 1b6444331beb ("mm/khugepaged: enable clean pagecache folio collapse for writable files") >> Cc: stable@vger.kernel.org >> Reported-by: Josef Bacik >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/truncate.c | 17 +++++++++++++++-- >> 1 file changed, 15 insertions(+), 2 deletions(-) >> >> diff --git a/mm/truncate.c b/mm/truncate.c >> index 733d2713a875a..6d8c0ec4623fe 100644 >> --- a/mm/truncate.c >> +++ b/mm/truncate.c >> @@ -499,7 +499,15 @@ void truncate_inode_pages_range(struct address_space *mapping, >> folio_lock(folio); >> VM_BUG_ON_FOLIO(!folio_contains(folio, indices[i]), folio); >> folio_wait_writeback(folio); >> - truncate_inode_folio(mapping, folio); >> + if (truncate_inode_folio(mapping, folio)) { >> + folio_unlock(folio); >> + /* >> + * Folio might have been replaced: look it up >> + * again. >> + */ >> + index = indices[i]; >> + break; >> + } >> folio_unlock(folio); >> } >> truncate_folio_batch_exceptionals(mapping, &fbatch, indices); > > This hunk looks unneeded to me: its second loop restarts from start > until find_get_entries() finds nothing, so the new folio gets truncated > on a later round. Or am I missing a case? For truncate_inode_pages_range() I *think* the "index >= end" might prevent another lookup that we would need. Assume we have a large folio with 512 pages for simplicity, and we want to punch-hole the first half of it. The whole partial splitting logic (truncate_inode_partial_folio) will first split that folio buddy-like into various folios. Now we want to remove the split folios in the loop: index = 0; end = 256; while (index < 256) if (!find_get_entries(mapping, &index, 255, &fbatch, ... -> Returns our split folios from the buddy split, the last one should cover pages 128 to 255 -> Sets index = 256 Then we have the concurrent stuff happening. We wouldn't re-execute the find_get_entries() even though a folio was replaced in the meantime, as index =256. My brain hurts, does the above make sense? -- Cheers, David