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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C8A4EC433FE for ; Tue, 19 Oct 2021 18:30:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF47F6137F for ; Tue, 19 Oct 2021 18:30:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234770AbhJSScN (ORCPT ); Tue, 19 Oct 2021 14:32:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36194 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232144AbhJSScN (ORCPT ); Tue, 19 Oct 2021 14:32:13 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12D57C06161C; Tue, 19 Oct 2021 11:30:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GZ9xrxMcNRI8ZuFFAy2iTPbxahYga2XstNQpPO9cMgE=; b=cn4Pc1pEaoHMVy8gIsrUIPBp6n IvhYVvPxLOGXmopmvPBIi8Z01toSzSmWvibfLFkBjdaHyUYJOrxR08qrwOT8UZ0xqUlec+T5luiVg GzIFfFKh4dwXqT/lDoAJASJwu3IC6cN7Nd7fTUc4kJHy6UjU9MOVZASY6Q/pq5RXGcHm+wZiqO5xJ L7mBvfVKYZM/Ih213xkdpm9shfhx35HfA4lgljh8ZVAEeC0fdP+lXyV7QW2BHwjDKms8f+xacEzUx RYX/9mTfEdCpiyeJAUYH1Hz1l6jJXF6KG6nNRl9qXwdGZU88BN3vWFIH5MDv87MotH6YVNyhJZwtM Byq3EC8w==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mctqE-00Bvpr-F1; Tue, 19 Oct 2021 18:28:14 +0000 Date: Tue, 19 Oct 2021 19:28:02 +0100 From: Matthew Wilcox To: David Howells Cc: linux-cachefs@redhat.com, Kent Overstreet , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , Alexander Viro , Omar Sandoval , Linus Torvalds , linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/67] mm: Stop filemap_read() from grabbing a superfluous page Message-ID: References: <163456861570.2614702.14754548462706508617.stgit@warthog.procyon.org.uk> <163456863216.2614702.6384850026368833133.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <163456863216.2614702.6384850026368833133.stgit@warthog.procyon.org.uk> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Oct 18, 2021 at 03:50:32PM +0100, David Howells wrote: > @@ -2625,6 +2625,10 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, > if ((iocb->ki_flags & IOCB_WAITQ) && already_read) > iocb->ki_flags |= IOCB_NOWAIT; > > + isize = i_size_read(inode); > + if (unlikely(iocb->ki_pos >= isize)) > + goto put_pages; > + Is there a good reason to assign to isize here? I'd rather not, because it complicates analysis, and a later change might look at the isize read here, not realising it was a racy use. So I'd rather see: if (unlikely(iocb->ki_pos >= i_size_read(inode))) goto put_pages;