From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757543AbbIDIOM (ORCPT ); Fri, 4 Sep 2015 04:14:12 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:37063 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750864AbbIDIOB (ORCPT ); Fri, 4 Sep 2015 04:14:01 -0400 Date: Fri, 4 Sep 2015 10:13:58 +0200 From: Michal Hocko To: Andy Grover Cc: hjk@hansjkoch.de, Greg KH , linux-kernel Subject: Re: __might_sleep in uio_read()? Message-ID: <20150904081358.GA8220@dhcp22.suse.cz> References: <55E77BF6.9000109@redhat.com> <20150903122616.GA17976@dhcp22.suse.cz> <55E895C6.5020305@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55E895C6.5020305@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 Thu 03-09-15 11:47:34, 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? --- >>From f50005095a90d21f628d8ce6525b432f17c8138c Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Fri, 4 Sep 2015 10:08:18 +0200 Subject: [PATCH] uio: fix false positive __might_sleep warning splat Andy has reported a __might_sleep warning [ 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] [ 5174.885198] Modules linked in: tcm_loop target_core_user uio target_core_pscsi target_core_file target_core_iblock iscsi_target_mod target_core_mod uinput fuse nfsv3 nfs_acl nfs lockd grace fscache sunrpc microcode i2c_piix4 virtio_balloon i2c_core xfs libcrc32c crc32c_intel virtio_net virtio_blk [ 5174.887351] CPU: 0 PID: 1532 Comm: tcmu-runner Not tainted 4.2.0-rc7+ [ 5174.887853] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014 [ 5174.888633] ffffffff81a3b870 ffff880045393ca8 ffffffff817afaae 0000000000000000 [ 5174.889224] ffff880045393cf8 ffff880045393ce8 ffffffff8109a846 ffff880045393cd8 [ 5174.889793] ffffffffa02a7150 00000000000002dc 0000000000000000 ffff880045008000 [ 5174.890375] Call Trace: [ 5174.890562] [] dump_stack+0x4c/0x65 [ 5174.890938] [] warn_slowpath_common+0x86/0xc0 [ 5174.891388] [] warn_slowpath_fmt+0x46/0x50 [ 5174.891808] [] ? uio_read+0x91/0x170 [uio] [ 5174.892237] [] ? uio_read+0x91/0x170 [uio] [ 5174.892653] [] __might_sleep+0x7d/0x90 [ 5174.893055] [] __might_fault+0x43/0xa0 [ 5174.893448] [] ? schedule+0x3e/0x90 [ 5174.893820] [] uio_read+0x132/0x170 [uio] [ 5174.894240] [] ? wake_up_q+0x70/0x70 [ 5174.894620] [] __vfs_read+0x28/0xe0 [ 5174.894993] [] ? security_file_permission+0xa3/0xc0 [ 5174.895541] [] ? rw_verify_area+0x4f/0xf0 [ 5174.896006] [] vfs_read+0x8a/0x140 [ 5174.896391] [] ? __schedule+0x425/0xcc0 [ 5174.896788] [] SyS_read+0x49/0xb0 The warning is a false positive because uio_read doesn't depent on TASK_INTERRUPTIBLE after copy_to_user so it is safe to silence the warning by an explicit setting the state to TASK_RUNNING in the path which might call into TASK_RUNNING. Reported-by: Andy Grover Signed-off-by: Michal Hocko --- drivers/uio/uio.c | 1 + 1 file changed, 1 insertion(+) 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 { -- 2.5.0 -- Michal Hocko SUSE Labs