From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755255AbbICM0V (ORCPT ); Thu, 3 Sep 2015 08:26:21 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:34629 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754695AbbICM0S (ORCPT ); Thu, 3 Sep 2015 08:26:18 -0400 Date: Thu, 3 Sep 2015 14:26:16 +0200 From: Michal Hocko To: Andy Grover Cc: hjk@hansjkoch.de, Greg KH , linux-kernel Subject: Re: __might_sleep in uio_read()? Message-ID: <20150903122616.GA17976@dhcp22.suse.cz> References: <55E77BF6.9000109@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55E77BF6.9000109@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 02-09-15 15:45:10, Andy Grover wrote: > Hi Hans and Greg, > > Is this an issue with uio? I swear it didn't used to throw this warning... > > Thanks -- Andy > > [ 5174.883261] ------------[ cut here ]------------ > [ 5174.883617] WARNING: CPU: 0 PID: 1532 at > /home/agrover/git/kernel/kernel/sched/core.c:7389 __might_sleep+0x7d/0x90() > [ 5174.884407] do not call blocking ops when !TASK_RUNNING; state=1 set at > [] uio_read+0x91/0x170 [uio] The warning says that the driver is calling copy_to_user with TASK_INTERRUPTIBLE which is wrong in general because this context can sleep and a schedule would destroy the state. It doesn't matter here because the code would break out from the loop regardless of the copy_to_user return value. I assume that TASK_INTERRUPTIBLE is necessary before the event_count check to prevent from wake up races. If that is the case then you can simply do: diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c index 3257d4220d01..7d8959e3833b 100644 --- a/drivers/uio/uio.c +++ b/drivers/uio/uio.c @@ -524,6 +524,7 @@ static ssize_t uio_read(struct file *filep, char __user *buf, event_count = atomic_read(&idev->event); if (event_count != listener->event_count) { + __set_current_state(TASK_RUNNING); if (copy_to_user(buf, &event_count, count)) retval = -EFAULT; else { -- Michal Hocko SUSE Labs