From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) (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 6C4E1246784 for ; Fri, 16 Oct 2026 09:57:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.110 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792144683; cv=none; b=TDlM8/t+BXNeim2bOqqH9UtnOm8KvujFDGcN/UMun2xCN0TJPcn0c7sMuq6zq5w+kdJqhvFN6zP3wpaQK3X+tmzRLVBjHH/LYavTZxtNrnOCB4mlf1/TjnxBDDbho0MbBW9zPZ2dl7PTx23PsffFGSwmp3wd0eYcKCbyb09XXj4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792144683; c=relaxed/simple; bh=g/ue6j42PAMVBFYKRRP/60F/c70PufirmsQ+SYOrazk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UbnowcY0DxcDopSaF89nkePrPWLi5dWuoip889JVubSGABxkngSuc0QvavLP9A5sgMKb9TzOavjObeBMdsoOcKmylRUaQ9JYVGiZA3k6wP9GZAEKo18+bJ2C0+Lfe8dQV7j1cDrEgJ/0KwuqLsFj5GvdMqpkFhfzbNvUvXf5weo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=s2coRmpL; arc=none smtp.client-ip=115.124.30.110 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="s2coRmpL" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1792144672; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=hAt144Vk7k8qMXgrEGhDpPZonayJjWzttOQo4WX8s+E=; b=s2coRmpLq7mOznbe57IIu547L90JOB/Ts/7ngvo436tPI2nSB71mqltBuGSKTX0EkPIaqguktWB0nISuvmtZ1TsYBqeqXwKfOf7xxsl8Zrt+y2CaqRjfV6VJhk5dCIHaRagXyDiKjv+lFhCOqoMj6RADRJmOr4iaWuB2Run4K+s= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R481e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045098064;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=21;SR=0;TI=SMTPD_---0XCuU.YY_1792144668; Received: from 30.74.144.163(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCuU.YY_1792144668 cluster:ay36) by smtp.aliyun-inc.com; Fri, 16 Oct 2026 17:57:49 +0800 Message-ID: <27e5aadc-2d68-428f-a958-308e4a75c058@linux.alibaba.com> Date: Fri, 16 Oct 2026 17:57:48 +0800 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 v3 1/1] khugepaged: fix readahead lock inversion in collapse_file() To: Lance Yang , akpm@linux-foundation.org Cc: david@kernel.org, ziy@nvidia.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, jack@suse.cz, djwong@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, hch@lst.de, syzbot+16bf7cd0ebeb1de93aa5@syzkaller.appspotmail.com, ngocthang2710.1999@gmail.com, willy@infradead.org, rppt@kernel.org, ljs@kernel.org References: <20261016065920.4153-1-lance.yang@linux.dev> From: Baolin Wang In-Reply-To: <20261016065920.4153-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/16/26 2:59 PM, Lance Yang wrote: > collapse_file() can end up calling page_cache_sync_readahead() with > source folios from earlier in the range still locked. If truncate already > holds mapping->invalidate_lock exclusively and is waiting for one of > those folios, readahead blocks on the same invalidate_lock and neither > side can make progress. > > Do readahead in a separate pass before we start holding source folios > locked for collapse. Keep page_cache_sync_readahead() and its existing > policy, and drop each folio's lock and reference after checking that it > is uptodate. If truncate or reclaim removes a folio between the two > passes, roll back instead of doing readahead again with source folios > locked. > > Shmem handles swapin and fallocated folios through shmem_get_folio() > without taking mapping->invalidate_lock, so it isn't affected by this > lock inversion. > > Reported-by: syzbot+16bf7cd0ebeb1de93aa5@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=16bf7cd0ebeb1de93aa5 > Fixes: 730633f0b7f9 ("mm: Protect operations adding pages to page cache with invalidate_lock") > Signed-off-by: Lance Yang > --- Thanks for the fix. > Thanks to Nguyen Ngoc Thang for v2. David asked for volunteers, so I'm > happy to take this over. > > Some older stable trees lack the folio infrastructure used here, and the > code will differ for each stable tree, so each backport will need quite a > bit of rework and its own review. I'm not sure whether to Cc stable here. > Once we agree on the fix, I'll send a separate backport for each maintained > stable tree except 5.10, which isn't affected. > > v2 -> v3: > - Replace the scan-wide invalidate_lock and page_cache_ra_unbounded() with > a preparation pass using page_cache_sync_readahead(). > - Roll back on a new page cache miss during collapse. > - https://lore.kernel.org/all/20260913163644.122133-1-ngocthang2710.1999@gmail.com/ > > mm/khugepaged.c | 42 +++++++++++++++++++++++++++++++----------- > 1 file changed, 31 insertions(+), 11 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index ef5cd6fda34f..b3f67617caf0 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2262,6 +2262,34 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > new_folio->index = start; > new_folio->mapping = mapping; > > + if (!is_shmem) { > + /* > + * Populate the range before accumulating locked source folios: > + * readahead may block on invalidate_lock. > + */ > + for (index = start; index < end;) { why drop xas_unlock_irq()? > + folio = filemap_lock_folio(mapping, index); > + if (IS_ERR(folio)) { > + page_cache_sync_readahead(mapping, &file->f_ra, > + file, index, end - index); > + folio = filemap_lock_folio(mapping, index); > + if (IS_ERR(folio)) { > + result = SCAN_FAIL; > + goto rollback; > + } > + } > + if (!folio_test_uptodate(folio)) > + result = SCAN_FAIL; Do we need to check PG_uptodate after locking the folio? If we successfully lock the folio, doesn't that mean the read I/O has completed? The following code also checks the writeback flag, so the uptodate check seems unnecessary to me. > + index = folio_next_index(folio); > + folio_unlock(folio); > + folio_put(folio); > + if (result != SCAN_SUCCEED) > + goto rollback; > + } > + /* drain lru cache to help folio_isolate_lru() */ > + lru_add_drain(); > + } Could we factor this code out into a small helper? > + > /* > * Ensure we have slots for all the pages in the range. This is > * almost certainly a no-op because most of the pages must be present > @@ -2320,17 +2348,9 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > } > } else { /* !is_shmem */ > if (!folio || xa_is_value(folio)) { > - xas_unlock_irq(&xas); > - page_cache_sync_readahead(mapping, &file->f_ra, > - file, index, > - end - index); > - /* drain lru cache to help folio_isolate_lru() */ > - lru_add_drain(); > - folio = filemap_lock_folio(mapping, index); > - if (IS_ERR(folio)) { > - result = SCAN_FAIL; > - goto xa_unlocked; > - } > + /* The range changed after the preparation pass. */ > + result = SCAN_PAGE_LOCK; > + goto xa_locked; > } else if (folio_test_dirty(folio)) { > /* > * This page is dirty because it hasn't