From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C8CBC282D8 for ; Wed, 30 Jan 2019 12:45:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63FD22184D for ; Wed, 30 Jan 2019 12:45:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730894AbfA3MpQ (ORCPT ); Wed, 30 Jan 2019 07:45:16 -0500 Received: from mx2.suse.de ([195.135.220.15]:41406 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727946AbfA3MpP (ORCPT ); Wed, 30 Jan 2019 07:45:15 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 41B7BAE88; Wed, 30 Jan 2019 12:45:13 +0000 (UTC) From: Vlastimil Babka To: Andrew Morton , Linus Torvalds Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Peter Zijlstra , Greg KH , Jann Horn , Jiri Kosina , Dominique Martinet , Andy Lutomirski , Dave Chinner , Kevin Easton , Matthew Wilcox , Cyril Hrubis , Tejun Heo , "Kirill A . Shutemov" , Daniel Gruss , Vlastimil Babka , Jiri Kosina Subject: [PATCH 2/3] mm/filemap: initiate readahead even if IOCB_NOWAIT is set for the I/O Date: Wed, 30 Jan 2019 13:44:19 +0100 Message-Id: <20190130124420.1834-3-vbabka@suse.cz> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190130124420.1834-1-vbabka@suse.cz> References: <20190130124420.1834-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jiri Kosina preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache contents, as it reveals metadata about residency of pages in pagecache. If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page not resident" information, and vice versa. Close that sidechannel by always initiating readahead on the cache if we encounter a cache miss for preadv2(RWF_NOWAIT); with that in place, probing the pagecache residency itself will actually populate the cache, making the sidechannel useless. Originally-by: Linus Torvalds Cc: Dominique Martinet Cc: Andy Lutomirski Cc: Dave Chinner Cc: Kevin Easton Cc: Matthew Wilcox Cc: Cyril Hrubis Cc: Tejun Heo Cc: Kirill A. Shutemov Cc: Daniel Gruss Signed-off-by: Jiri Kosina Signed-off-by: Vlastimil Babka --- mm/filemap.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 9f5e323e883e..7bcdd36e629d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2075,8 +2075,6 @@ static ssize_t generic_file_buffered_read(struct kiocb *iocb, page = find_get_page(mapping, index); if (!page) { - if (iocb->ki_flags & IOCB_NOWAIT) - goto would_block; page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); -- 2.20.1