From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
To: lkp@lists.01.org
Subject: Re: [writeback] 8bc4ad9498: INFO: suspicious RCU usage. ]
Date: Fri, 02 Sep 2016 10:00:56 -0700 [thread overview]
Message-ID: <20160902170056.GN16261@linux.vnet.ibm.com> (raw)
In-Reply-To: <1a774b3f-9fdc-b620-9a35-d3e7ff18177a@fb.com>
[-- Attachment #1: Type: text/plain, Size: 3583 bytes --]
On Fri, Sep 02, 2016 at 09:49:25AM -0600, Jens Axboe wrote:
> On 09/02/2016 09:36 AM, Paul E. McKenney wrote:
> >On Fri, Sep 02, 2016 at 10:56:22AM -0400, Tejun Heo wrote:
> >>(cc'ing Paul, hi!)
> >>
> >>Hello,
> >>
> >>On Thu, Sep 01, 2016 at 02:13:34PM -0600, Jens Axboe wrote:
> >>>On 09/01/2016 04:21 AM, kernel test robot wrote:
> >>>>[ 7.323356] cdrom: Uniform CD-ROM driver Revision: 3.20
> >>>>[ 7.334239]
> >>>>[ 7.337256] ===============================
> >>>>[ 7.340532] [ INFO: suspicious RCU usage. ]
> >>>>[ 7.342419] 4.8.0-rc4-00008-g8bc4ad9 #1 Not tainted
> >>>>[ 7.347065] -------------------------------
> >>>>[ 7.350132] include/linux/cgroup.h:435 suspicious rcu_dereference_check() usage!
> >
> >Lockdep does not believe that any locks are held, correct?
>
> Which is correct, the queue lock has been dropped at this point.
Note that lockdep believes that the rcu_read_lock() has also been
dropped, otherwise it would have listed it.
> >>>>[ 7.410074] Call Trace:
> >>>>[ 7.411328] [<ffffffff8178ed3b>] dump_stack+0x82/0xb8
> >>>>[ 7.413982] [<ffffffff81123472>] lockdep_rcu_suspicious+0xf7/0x100
> >>>>[ 7.415828] [<ffffffff817873f4>] bio_blkcg+0x89/0x93
> >>>>[ 7.417336] [<ffffffff817891f0>] check_blkcg_changed+0x58/0x1b8
> >>>>[ 7.428722] [<ffffffff81789b90>] cfq_set_request+0xd1/0x2a3
> >>>>[ 7.439690] [<ffffffff81763fe3>] elv_set_request+0x1f/0x24
> >>>>[ 7.442157] [<ffffffff8176856d>] get_request+0x38f/0x77f
> >>>>[ 7.447449] [<ffffffff817689c2>] blk_get_request+0x65/0xa8
> >>>>[ 7.449868] [<ffffffff81c692df>] ide_cd_queue_pc+0x76/0x19d
> >>>>[ 7.453757] [<ffffffff81c695ee>] cdrom_check_status+0x51/0x53
> >>>>[ 7.455372] [<ffffffff81c6a27e>] ide_cdrom_check_events_real+0x20/0x3f
> >>>>[ 7.457294] [<ffffffff82579f94>] cdrom_update_events+0x18/0x21
> >>>>[ 7.458987] [<ffffffff82579faf>] cdrom_check_events+0x12/0x1f
> >>>>[ 7.460713] [<ffffffff81c68317>] idecd_check_events+0x1c/0x1e
> >>>>[ 7.462393] [<ffffffff81778d12>] disk_check_events+0x47/0x103
> >>>>[ 7.464129] [<ffffffff81778dea>] disk_events_workfn+0x1c/0x1e
> >>>>[ 7.465844] [<ffffffff810fcafa>] process_one_work+0x272/0x4ee
> >>>>[ 7.467462] [<ffffffff810fd247>] worker_thread+0x1eb/0x2c9
> >>
> >>The warning is from
> >>
> >>#define task_css_set_check(task, __c) \
> >> rcu_dereference_check((task)->cgroups, \
> >> lockdep_is_held(&cgroup_mutex) || \
> >> lockdep_is_held(&css_set_lock) || \
> >> ((task)->flags & PF_EXITING) || (__c))
> >>
> >>which is used by bio_blkcg() which is called by the following code in
> >>check_blkcg_changed().
> >>
> >> rcu_read_lock();
> >> serial_nr = bio_blkcg(bio)->css.serial_nr;
> >> rcu_read_unlock();
> >>
> >>So, I have no idea. It looks like rcu_dereference_check() is being
> >>called with rcu read locked but still triggering suspicious RCU usage
> >>warning.
> >
> >Perhaps there is an rcu_read_unlock() somewhere on the code path?
> >
> >>The code hasn't changed for quite a while now, so it's also really
> >>weird that it's triggering now. Paul, does anything ring a bell?
> >
> >I have not see something like this recently.
>
> The question is if it's really new, or just re-triggering because the
> writeback branch changes that function? It's further down though, so
> can't impact the RCU section. And the writeback changes don't have any
> RCU code in them...
At this point, I have to suggest "git bisect"...
Thanx, Paul
WARNING: multiple messages have this Message-ID (diff)
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Jens Axboe <axboe@fb.com>
Cc: Tejun Heo <tj@kernel.org>,
kernel test robot <xiaolong.ye@intel.com>,
lkp@01.org, Jens Axboe <axboe@kernel.dk>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [writeback] 8bc4ad9498: INFO: suspicious RCU usage. ]
Date: Fri, 2 Sep 2016 10:00:56 -0700 [thread overview]
Message-ID: <20160902170056.GN16261@linux.vnet.ibm.com> (raw)
In-Reply-To: <1a774b3f-9fdc-b620-9a35-d3e7ff18177a@fb.com>
On Fri, Sep 02, 2016 at 09:49:25AM -0600, Jens Axboe wrote:
> On 09/02/2016 09:36 AM, Paul E. McKenney wrote:
> >On Fri, Sep 02, 2016 at 10:56:22AM -0400, Tejun Heo wrote:
> >>(cc'ing Paul, hi!)
> >>
> >>Hello,
> >>
> >>On Thu, Sep 01, 2016 at 02:13:34PM -0600, Jens Axboe wrote:
> >>>On 09/01/2016 04:21 AM, kernel test robot wrote:
> >>>>[ 7.323356] cdrom: Uniform CD-ROM driver Revision: 3.20
> >>>>[ 7.334239]
> >>>>[ 7.337256] ===============================
> >>>>[ 7.340532] [ INFO: suspicious RCU usage. ]
> >>>>[ 7.342419] 4.8.0-rc4-00008-g8bc4ad9 #1 Not tainted
> >>>>[ 7.347065] -------------------------------
> >>>>[ 7.350132] include/linux/cgroup.h:435 suspicious rcu_dereference_check() usage!
> >
> >Lockdep does not believe that any locks are held, correct?
>
> Which is correct, the queue lock has been dropped at this point.
Note that lockdep believes that the rcu_read_lock() has also been
dropped, otherwise it would have listed it.
> >>>>[ 7.410074] Call Trace:
> >>>>[ 7.411328] [<ffffffff8178ed3b>] dump_stack+0x82/0xb8
> >>>>[ 7.413982] [<ffffffff81123472>] lockdep_rcu_suspicious+0xf7/0x100
> >>>>[ 7.415828] [<ffffffff817873f4>] bio_blkcg+0x89/0x93
> >>>>[ 7.417336] [<ffffffff817891f0>] check_blkcg_changed+0x58/0x1b8
> >>>>[ 7.428722] [<ffffffff81789b90>] cfq_set_request+0xd1/0x2a3
> >>>>[ 7.439690] [<ffffffff81763fe3>] elv_set_request+0x1f/0x24
> >>>>[ 7.442157] [<ffffffff8176856d>] get_request+0x38f/0x77f
> >>>>[ 7.447449] [<ffffffff817689c2>] blk_get_request+0x65/0xa8
> >>>>[ 7.449868] [<ffffffff81c692df>] ide_cd_queue_pc+0x76/0x19d
> >>>>[ 7.453757] [<ffffffff81c695ee>] cdrom_check_status+0x51/0x53
> >>>>[ 7.455372] [<ffffffff81c6a27e>] ide_cdrom_check_events_real+0x20/0x3f
> >>>>[ 7.457294] [<ffffffff82579f94>] cdrom_update_events+0x18/0x21
> >>>>[ 7.458987] [<ffffffff82579faf>] cdrom_check_events+0x12/0x1f
> >>>>[ 7.460713] [<ffffffff81c68317>] idecd_check_events+0x1c/0x1e
> >>>>[ 7.462393] [<ffffffff81778d12>] disk_check_events+0x47/0x103
> >>>>[ 7.464129] [<ffffffff81778dea>] disk_events_workfn+0x1c/0x1e
> >>>>[ 7.465844] [<ffffffff810fcafa>] process_one_work+0x272/0x4ee
> >>>>[ 7.467462] [<ffffffff810fd247>] worker_thread+0x1eb/0x2c9
> >>
> >>The warning is from
> >>
> >>#define task_css_set_check(task, __c) \
> >> rcu_dereference_check((task)->cgroups, \
> >> lockdep_is_held(&cgroup_mutex) || \
> >> lockdep_is_held(&css_set_lock) || \
> >> ((task)->flags & PF_EXITING) || (__c))
> >>
> >>which is used by bio_blkcg() which is called by the following code in
> >>check_blkcg_changed().
> >>
> >> rcu_read_lock();
> >> serial_nr = bio_blkcg(bio)->css.serial_nr;
> >> rcu_read_unlock();
> >>
> >>So, I have no idea. It looks like rcu_dereference_check() is being
> >>called with rcu read locked but still triggering suspicious RCU usage
> >>warning.
> >
> >Perhaps there is an rcu_read_unlock() somewhere on the code path?
> >
> >>The code hasn't changed for quite a while now, so it's also really
> >>weird that it's triggering now. Paul, does anything ring a bell?
> >
> >I have not see something like this recently.
>
> The question is if it's really new, or just re-triggering because the
> writeback branch changes that function? It's further down though, so
> can't impact the RCU section. And the writeback changes don't have any
> RCU code in them...
At this point, I have to suggest "git bisect"...
Thanx, Paul
next prev parent reply other threads:[~2016-09-02 17:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-01 10:21 [writeback] 8bc4ad9498: INFO: suspicious RCU usage. ] kernel test robot
2016-09-01 10:21 ` kernel test robot
2016-09-01 20:13 ` Jens Axboe
2016-09-01 20:13 ` Jens Axboe
2016-09-02 14:56 ` Tejun Heo
2016-09-02 14:56 ` Tejun Heo
2016-09-02 15:36 ` Paul E. McKenney
2016-09-02 15:36 ` Paul E. McKenney
2016-09-02 15:49 ` Jens Axboe
2016-09-02 15:49 ` Jens Axboe
2016-09-02 17:00 ` Paul E. McKenney [this message]
2016-09-02 17:00 ` Paul E. McKenney
2016-09-02 18:00 ` Tejun Heo
2016-09-02 18:00 ` Tejun Heo
2016-09-07 16:41 ` Tejun Heo
2016-09-07 16:41 ` Tejun Heo
2016-09-07 19:25 ` Jens Axboe
2016-09-07 19:25 ` Jens Axboe
2016-09-08 1:43 ` Fengguang Wu
2016-09-08 1:43 ` [LKP] " Fengguang Wu
2016-09-08 2:04 ` Ye Xiaolong
2016-09-08 2:04 ` [LKP] " Ye Xiaolong
2016-09-08 15:52 ` Jens Axboe
2016-09-08 15:52 ` [LKP] " Jens Axboe
2016-09-09 0:46 ` Ye Xiaolong
2016-09-09 0:46 ` [LKP] " Ye Xiaolong
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