From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934022AbcIEOCs (ORCPT ); Mon, 5 Sep 2016 10:02:48 -0400 Received: from forwardcorp1o.cmail.yandex.net ([37.9.109.47]:37010 "EHLO forwardcorp1o.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932413AbcIEOCr (ORCPT ); Mon, 5 Sep 2016 10:02:47 -0400 Authentication-Results: smtpcorp1p.mail.yandex.net; dkim=pass header.i=@yandex-team.ru Subject: Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs To: Greg Kroah-Hartman , Konstantin Khlebnikov References: <146662093622.3726.10220135910756738018.stgit@buzz> <20160905134628.GA30206@kroah.com> Cc: Linux Kernel Mailing List , NeilBrown , Tejun Heo , Stable , Alexander Viro From: Konstantin Khlebnikov Message-ID: Date: Mon, 5 Sep 2016 17:02:43 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160905134628.GA30206@kroah.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.09.2016 16:46, Greg Kroah-Hartman wrote: > On Mon, Sep 05, 2016 at 04:25:48PM +0300, Konstantin Khlebnikov wrote: >> Bump > > Huh? > >> On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov >> wrote: >>> Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns >>> zero bytes for non-zero offset. This breaks script checkarray in mdadm tool >>> in debian where /bin/sh is 'dash' because its builtin 'read' reads only one >>> byte at a time. Script gets 'i' instead of 'idle' when reads current action >>> from /sys/block/$dev/md/sync_action and as a result does nothing. >>> >>> This patch adds trivial implementation of partial read: generate whole >>> string and move required part into buffer head. >>> >>> Signed-off-by: Konstantin Khlebnikov >>> Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.") >>> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950 >>> Cc: Stable # v3.19+ >>> --- >>> fs/sysfs/file.c | 8 +++++++- >>> 1 file changed, 7 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c >>> index f35523d4fa3a..b803213d1307 100644 >>> --- a/fs/sysfs/file.c >>> +++ b/fs/sysfs/file.c >>> @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf, >>> * If buf != of->prealloc_buf, we don't know how >>> * large it is, so cannot safely pass it to ->show >>> */ >>> - if (pos || WARN_ON_ONCE(buf != of->prealloc_buf)) >>> + if (WARN_ON_ONCE(buf != of->prealloc_buf)) >>> return 0; >>> len = ops->show(kobj, of->kn->priv, buf); >>> + if (pos) { >>> + if (len <= pos) >>> + return 0; >>> + len -= pos; >>> + memmove(buf, buf + pos, len); >>> + } >>> return min(count, len); >>> } > > I don't have this in any queue of mine, so I don't understand what you > are asking about. > > totally confused, > Well.. One user poked me about this bug. Patch was Acked-by: Tejun Heo get_maintainer.pl points to you but probably this more VFS problem. so... this time I've added Al into CC Should I resend patch once again, or this very trivial but pretty dangerous problem could be solved without this? IIRR this breaks automatic recheck of MD RAIDs for all debian-based systems -- Konstantin