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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38BDFC433EF for ; Sat, 11 Jun 2022 13:44:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233638AbiFKNoE (ORCPT ); Sat, 11 Jun 2022 09:44:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45898 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231393AbiFKNoB (ORCPT ); Sat, 11 Jun 2022 09:44:01 -0400 Received: from mail-pl1-x635.google.com (mail-pl1-x635.google.com [IPv6:2607:f8b0:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E002B4A4; Sat, 11 Jun 2022 06:44:00 -0700 (PDT) Received: by mail-pl1-x635.google.com with SMTP id f9so1522106plg.0; Sat, 11 Jun 2022 06:44:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Ixh/tGjYEGtd9B0U4un+L2Dg2/GvxVifxx8JOO5/xxs=; b=dWFageSqD+a/p7/dg6peuXBetNvvozPq1OrZOQ/jnLrmOlYGPzNGQ4RjNm2jbazw9i u781rrcK5N+1rObNiGXHrWMqVQY7pZTTAMDXq7DNXEPeF453QBw6/bxOS0JTWBW4mEFL oUM/P6Tc2N9Ofg4sbBfsItn4mThyJNPYPK0dfcLnQTh5rjJPmndWQJuSTs7DAwaCi/Vx rL+jaeKda3xCTVgeOwll+wUPQ1XB4/3T0OO18jS1/nlZwt9iAYKwdDwzN6eMueoG9fyg LLwuRDA7jXNLhI6Pff6Xji5gCQ5vnnxkZEApvX0oXAyGKRCiRXSTKan8B5OV8LXdXJGh CGZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=Ixh/tGjYEGtd9B0U4un+L2Dg2/GvxVifxx8JOO5/xxs=; b=wXfDFrpYDnGpiJnabp8sN75w74M9E0Y8PzOb3H9hcO0MwIMY1UoXYS9gZgecAlipg/ P4t2ad522G9Jmha+shE3ydjXSt585sVGVllOVzPEuRPMPcWiAI5fkFyuRblI/PFi09cE PCVEXLTQMaFfb6n8Z4hqM5dbAcpUVcfqyKEIZxhDo/1H/iUN+TDRAGQElxYbq3zMan52 Bi0cyjOME63xd3YUimrMXVnN0pbh7M2iCTCqZJkAnIcHfU+8qrOqBsQo+rj6y0gyQvtB 3yLKcTZM8EqDnmhq3sssAN9Hro4vN54l1WzEIzYuQVhS19tY8sUc1pNWNSjkl6PmU6Xw bPMA== X-Gm-Message-State: AOAM530t+ot3f2XxpbZgzfbXzC/hnDSy1T3Q24Fw1FOOEtAXFy3QcckV 1ioMKzn1A6Kfl1Ovmi5/H6j+Y3DvhqU= X-Google-Smtp-Source: ABdhPJyVm1Qx3rpbnexbaPz3LjRNh5xdY5jWDRPJD5O1BPtSHpLAWd+II5ejGzWE9luF6mWKd4zRSA== X-Received: by 2002:a17:902:9f96:b0:163:dc33:6b72 with SMTP id g22-20020a1709029f9600b00163dc336b72mr50033692plq.34.1654955039652; Sat, 11 Jun 2022 06:43:59 -0700 (PDT) Received: from server.roeck-us.net ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id a12-20020a1709027e4c00b00164097a779fsm1523377pln.147.2022.06.11.06.43.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 11 Jun 2022 06:43:58 -0700 (PDT) Sender: Guenter Roeck Date: Sat, 11 Jun 2022 06:43:57 -0700 From: Guenter Roeck To: David Howells Cc: jlayton@kernel.org, Alexander Viro , Dominique Martinet , Mike Marshall , Gao Xiang , linux-afs@lists.infradead.org, v9fs-developer@lists.sourceforge.net, devel@lists.orangefs.org, linux-erofs@lists.ozlabs.org, linux-cachefs@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] iov_iter: Fix iter_xarray_get_pages{,_alloc}() Message-ID: <20220611134357.GA278954@roeck-us.net> References: <165476202136.3999992.433442175457370240.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <165476202136.3999992.433442175457370240.stgit@warthog.procyon.org.uk> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jun 09, 2022 at 09:07:01AM +0100, David Howells wrote: > The maths at the end of iter_xarray_get_pages() to calculate the actual > size doesn't work under some circumstances, such as when it's been asked to > extract a partial single page. Various terms of the equation cancel out > and you end up with actual == offset. The same issue exists in > iter_xarray_get_pages_alloc(). > > Fix these to just use min() to select the lesser amount from between the > amount of page content transcribed into the buffer, minus the offset, and > the size limit specified. > > This doesn't appear to have caused a problem yet upstream because network > filesystems aren't getting the pages from an xarray iterator, but rather > passing it directly to the socket, which just iterates over it. Cachefiles > *does* do DIO from one to/from ext4/xfs/btrfs/etc. but it always asks for > whole pages to be written or read. > > Fixes: 7ff5062079ef ("iov_iter: Add ITER_XARRAY") > Reported-by: Jeff Layton > Signed-off-by: David Howells > cc: Alexander Viro > cc: Dominique Martinet > cc: Mike Marshall > cc: Gao Xiang > cc: linux-afs@lists.infradead.org > cc: v9fs-developer@lists.sourceforge.net > cc: devel@lists.orangefs.org > cc: linux-erofs@lists.ozlabs.org > cc: linux-cachefs@redhat.com > cc: linux-fsdevel@vger.kernel.org > --- > > lib/iov_iter.c | 20 ++++---------------- > 1 file changed, 4 insertions(+), 16 deletions(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index 834e1e268eb6..814f65fd0c42 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -1434,7 +1434,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, > { > unsigned nr, offset; > pgoff_t index, count; > - size_t size = maxsize, actual; > + size_t size = maxsize; > loff_t pos; > > if (!size || !maxpages) > @@ -1461,13 +1461,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, > if (nr == 0) > return 0; > > - actual = PAGE_SIZE * nr; > - actual -= offset; > - if (nr == count && size > 0) { > - unsigned last_offset = (nr > 1) ? 0 : offset; > - actual -= PAGE_SIZE - (last_offset + size); > - } > - return actual; > + return min(nr * PAGE_SIZE - offset, maxsize); This needs min_t to avoid a build error on 32-bit builds. In file included from include/linux/kernel.h:26, from include/linux/crypto.h:16, from include/crypto/hash.h:11, from lib/iov_iter.c:2: lib/iov_iter.c: In function 'iter_xarray_get_pages': include/linux/minmax.h:20:35: error: comparison of distinct pointer types lacks a cast [-Werror] ... lib/iov_iter.c:1628:16: note: in expansion of macro 'min' 1628 | return min(nr * PAGE_SIZE - offset, maxsize); | ^~~ Guenter