From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793099173; b=W7ls8oH8qn4kJbovq33sOl9P/6JeH1M4F5dLpGCUOwlOPPpEhWboCTizY27UZC6u8YEQ vNAFnfngI3Om/Tb3D08SJ5Fr9wKBMd2detR0Ci6fihDRZc6Euo9RpxsJO+nM21HUGaEsg AIhPQY9TzMj7zzxFgZsc92exn5xBFHaRXUbjVZLIq4JkkxJPLOgEdOuAs7dfmxC3ANn9k QsD/vmEyr2ooWKZp77HX74XFzkOBkL8Daj6feKvI3TCYb5NsnPz42rCHk8S8+DvWj3qRQ TBqPxn7PBLA1Hql0zJEUaoyrWEjbal3aVYp8IOJ3ZzaOexPjO9bNQeEbqaYPKhks4GA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793099173; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=bD2dDAY20BKTrGXuNns0RrUfHKPHaCZasCXEiPto34g=; b=CtzNO3L9bW/QFwxoDH6xxHMZxaxxU1vtpwMRpWBbj6vQSe9nXD7Fgd70MBFOb6WnZjzV czrtF13K73JkHp1KXOZWAiOgFW1q9pKIDM1iMf+FqxqHSXYc3093BxUeXEjalwPT00Hy+ LrEd0wdrLoP8yWWxUa0fJxoIC7L43eIcJcxlhy35+hTbZ0UV49UC5LIokxQmhxMgmaIH2 5xO0KXQxEuEvOEtLkJiAK+I/dKJMLYfxWzUfjs4s1aPlQ3n3w1BmBHkWQGJViKqQYoeNH tF2jYZdqE+BZpirkRGfPa+8RlJVjURzsxlHhxtOfkCfPV3qxAh5RwFM0NxfuQaM12Pw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="HYHAo/Ox"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5BFFC606A329; Tue, 27 Oct 2026 11:06:13 +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=HYHAo/Ox Received: by smtp.kernel.org (Postfix) with ESMTPSA id 316F31F01825; Tue, 27 Oct 2026 11:06:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793099172; bh=bD2dDAY20BKTrGXuNns0RrUfHKPHaCZasCXEiPto34g=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HYHAo/Ox8MT7UXy2pq6W/phAJ2m1YIXIQBAFUZEX4uxXpNYFdXSnoSs1Q/b/g2AtH p3xkQ4a+4FH/jD2ZitM43gA20N3VlLtCejbxPvBm0pi5oWcnRM011ai7c6jDwdbVh/ GRzNPuWRA8hnOC1urxirDV01RQ6RF+GQ/B5OtYBpQYoYRiTQgTPcd3AJ27o+n89yip /z1GKaYCjadKjpubV8HMWLtzzSHg8uNQFroASMnpXLulLZbW4kWmEU0MD1ixxml377 SnfP+/l79Noo6REZlR+0vXakYK6vEpDc2OpC+QRwjA1gYWLcFzu9hNxeJyebzcpfuU mrxNKVhwbk0YQ== Message-ID: <321017a4-58cb-4178-8ff2-055a9bbb28b6@kernel.org> Date: Tue, 27 Oct 2026 12:06:05 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] khugepaged: fix readahead lock inversion in collapse_file() To: Lance Yang , akpm@linux-foundation.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.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, pfalcato@suse.de, ngocthang2710.1999@gmail.com, syzbot+16bf7cd0ebeb1de93aa5@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20261026152013.10511-1-lance.yang@linux.dev> 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 10/26/26 16:20, Lance Yang wrote: > collapse_file() can call page_cache_sync_readahead() while still holding > source folios locked. If truncate holds mapping->invalidate_lock > exclusively and waits for one of those folios, readahead waits for > invalidate_lock and neither side can make progress. > > We need to release those folio locks before starting readahead. On a page > cache miss, roll back first, populate the collapse range, and retry once. > Doing readahead after rollback avoids an extra pass when all folios are > already present. If another miss occurs on retry, give up rather than keep > retrying while truncate or reclaim removes folios. Makes sense. So we simply try readahead on all folios. Any reason we don't simply add a second loop after the first loop where we don't take the folio locks and do the swapin/readahead dance, then a second loop where we do all the other stuff? Then we don't need this fallback logic. -- Cheers, David