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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=n+WA9GNg; 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 28EBA606A31A; Tue, 27 Oct 2026 19:03:08 +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=n+WA9GNg Received: by smtp.kernel.org (Postfix) with ESMTPSA id B14991F031E3; Tue, 27 Oct 2026 19:03:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793127788; bh=z2aICW6ha5mvAYcJTiKr0lmuhUF+UbL5lXiLkXBjUAA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=n+WA9GNgsZok/1bfEEz2jnBVNjFM9RCPATbiZ3nZjEc4IWyk8DMWmdqf4y0yDp3Nk E7ZL/Uk8T+VM6ijsONiQbZMONfbqfABEznvjkqS6NgUU60Mz8R7vr7EWE6wSrS0cYu OwDmo+nIMCV2nM9WmqsKwoTKI9VkjrpzGRkq2CmRQVTwXunYfm/9QaVTXJx7P7tClw aQ3ETzz49IbbnD6kOa2Jki/Rp03R48LCJ8UDgkEJjnTqNzrU3WhDO3U8bTkL/ndP/V 3+OcMyuIwKPCmhg+/6GvyQ5ajb6AO5jG7HJepgBLRsF0SeSY/e0L7O0SIQavT4WGIk 5FZTSbuWwIhog== Message-ID: <331082ad-d8ad-40ec-a281-b9aee72a3f75@kernel.org> Date: Tue, 27 Oct 2026 20:03:00 +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. > > Keep page_cache_sync_readahead() and wait for read I/O with > filemap_lock_folio(), releasing each folio before moving to the next. The > existing uptodate check during collapse still handles read errors. > > Shmem uses shmem_get_folio() for swapin and fallocated folios without > taking mapping->invalidate_lock, so it is unaffected. > > 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") > Cc: stable@vger.kernel.org > Signed-off-by: Lance Yang > --- As discussed, this needs some rework afterwards. For now this should fix the problem Acked-by: David Hildenbrand (Arm) -- Cheers, David