From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f194.google.com ([209.85.220.194]:36777 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030323AbcIWPyO (ORCPT ); Fri, 23 Sep 2016 11:54:14 -0400 MIME-Version: 1.0 In-Reply-To: <1471943977-17822-1-git-send-email-tomasz.majchrzak@intel.com> References: <1471943977-17822-1-git-send-email-tomasz.majchrzak@intel.com> From: Dan Williams Date: Fri, 23 Sep 2016 08:54:12 -0700 Message-ID: Subject: Re: [PATCH] seq_file: don't set read position for invalid iterator To: Tomasz Majchrzak Cc: linux-fsdevel , aleksey.obitotskiy@intel.com, "Baldysiak, Pawel" , Artur Paszkiewicz , maksymilian.kunt@intel.com, Al Viro , Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-fsdevel-owner@vger.kernel.org List-ID: [ adding Al ] On Tue, Aug 23, 2016 at 2:19 AM, Tomasz Majchrzak wrote: > If kernfs file is empty on a first read, successive read operations > using the same file descriptor will return no data, even when data is > available. Default kernfs 'seq_next' implementation advances iterator > position even when next object is not there. Kernfs 'seq_start' for > following requests will not return iterator as position is already on > the second object. > > Don't set read position if valid iterator has not been returned. Can you say a bit about how you found this? So we have an idea about userspace tooling is broken by this bug. > > Signed-off-by: Tomasz Majchrzak I would add "Cc: " to the next version of this patch. > fs/seq_file.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/seq_file.c b/fs/seq_file.c > index 19f532e..893db43 100644 > --- a/fs/seq_file.c > +++ b/fs/seq_file.c > @@ -242,7 +242,8 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos) > m->count = 0; > if (unlikely(!m->count)) { > p = m->op->next(m, p, &pos); > - m->index = pos; > + if (p && !IS_ERR(p)) Lets change this to use the IS_ERR_OR_NULL() helper, and do the same with the earlier if (!p || IS_ERR()) a few lines up in the loop. Other than that, this looks good to me. Reviewed-by: Dan Williams