From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752683AbbICUMb (ORCPT ); Thu, 3 Sep 2015 16:12:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34264 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751093AbbICUM3 (ORCPT ); Thu, 3 Sep 2015 16:12:29 -0400 Subject: Re: __might_sleep in uio_read()? To: Greg KH References: <55E77BF6.9000109@redhat.com> <20150903122616.GA17976@dhcp22.suse.cz> <55E895C6.5020305@redhat.com> <20150903191239.GA31424@kroah.com> Cc: Michal Hocko , hjk@hansjkoch.de, linux-kernel From: Andy Grover Organization: Red Hat Message-ID: <55E8A9AC.9030709@redhat.com> Date: Thu, 3 Sep 2015 13:12:28 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20150903191239.GA31424@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 09/03/2015 12:12 PM, Greg KH wrote: > On Thu, Sep 03, 2015 at 11:47:34AM -0700, Andy Grover wrote: >> On 09/03/2015 05:26 AM, Michal Hocko wrote: >>> 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 { >>> >> >> This certainly makes the warning go away. If this looks good to everyone >> else can we get this change in? > > What changed to require this? Why is this suddenly showing up now? I'm working on drivers/target/target_core_user.c, a SCSI userspace passthrough that was added in 3.18, aka TCMU, which uses uio. The checks for !TASK_RUNNING were added in 3.19 (8eb23b9f3 and 00845eb96) ...and I'm just getting back to TCMU development after a bit, so maybe I'm the first one to call uio_read since those checks were added in 3.19? -- Andy