Date:	Sun, 27 Sep 2015 18:25:37 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL rcu/urgent] Fix two more 4.3 regressions

On Sun, Sep 27, 2015 at 6:16 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
> On Sun, Sep 27, 2015 at 6:02 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>> On Sun, Sep 27, 2015 at 5:58 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>>> On Sun, Sep 27, 2015 at 5:55 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>>>> On Sun, Sep 27, 2015 at 5:49 PM, Paul E. McKenney
>>>> <paulmck@...ux.vnet.ibm.com> wrote:
>>>>> On Sun, Sep 27, 2015 at 09:37:05AM +0200, Sedat Dilek wrote:
>>>>>> On Sun, Sep 27, 2015 at 9:32 AM, Paul E. McKenney
>>>>>> <paulmck@...ux.vnet.ibm.com> wrote:
>>>>>> > On Sun, Sep 27, 2015 at 08:28:39AM +0200, Sedat Dilek wrote:
>>>>>> >> Hi,
>>>>>> >>
>>>>>> >> as I have observed here some lockdep issues (one could be solved in
>>>>>> >> netdev) I wanted to try this patchset.
>>>>>> >>
>>>>>> >> Unfortunately, you cannot pull from...
>>>>>> >>
>>>>>> >> "These changes are available in the git repository at:
>>>>>> >>
>>>>>> >>   git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git for-mingo
>>>>>> >>
>>>>>> >> for you to fetch changes up to 19a5ecde086a6a5287978b12ae948fa691b197b7:
>>>>>> >>
>>>>>> >>   rcu: Suppress lockdep false positive for rcp->exp_funnel_mutex
>>>>>> >> (2015-09-20 21:01:22 -0700)
>>>>>> >>
>>>>>> >> ----------------------------------------------------------------
>>>>>> >> Oleg Nesterov (1):
>>>>>> >>       rcu: Change _wait_rcu_gp() to work around GCC bug 67055
>>>>>> >>
>>>>>> >> Paul E. McKenney (1):
>>>>>> >>       rcu: Suppress lockdep false positive for rcp->exp_funnel_mutex
>>>>>> >>
>>>>>> >>  include/linux/rcupdate.h | 11 +++++------
>>>>>> >>  kernel/rcu/tree.c        |  5 +++++
>>>>>> >>  2 files changed, 10 insertions(+), 6 deletions(-)"
>>>>>> >>
>>>>>> >> So, I have stolen them from linux-next.git.
>>>>>> >>
>>>>>> >> Please look at this, Thanks.
>>>>>> >
>>>>>> > Does it work better now?  (Forgot to actually push the new name...)
>>>>>>
>>>>>> Hi Paul,
>>>>>>
>>>>>> now for-mingo Git branch has this two fixes.
>>>>>
>>>>> Whew!!!  Apologies for the hassle!
>>>>>
>>>>>> I just booted into my new kernel with the "stolen" rcu.fixes from -next.
>>>>>>
>>>>>> For the lockdep problems I will do a CONFIG_DEBUG_LOCKDEP=y to see if
>>>>>> I get some more infos on the workqueue trouble.
>>>>>>
>>>>>> [   23.874836] BUG: sleeping function called from invalid context at
>>>>>> kernel/workqueue.c:2678
>>>>>> [   23.874902] in_atomic(): 0, irqs_disabled(): 1, pid: 1411, name: acpid
>>>>>
>>>>> Did you get a stack trace?  There are quite a few potential callers of
>>>>> start_flush_work() via flush_work().
>>>>>
>>>>
>>>> Hi Paul :-),
>>>>
>>>> Here is the stack trace.
>>>>
>>>> [   23.045871] BUG: sleeping function called from invalid context at
>>>> kernel/workqueue.c:2678
>>>> [   23.045982] in_atomic(): 0, irqs_disabled(): 1, pid: 1399, name: acpid
>>>> [   23.046064] 3 locks held by acpid/1399:
>>>> [   23.046066]  #0:  (&evdev->mutex){+.+...}, at: [<ffffffff8174ac7c>]
>>>> evdev_release+0xbc/0xf0
>>>> [   23.046081]  #1:  (&dev->mutex#2){+.+...}, at: [<ffffffff81742397>]
>>>> input_close_device+0x27/0x70
>>>> [   23.046093]  #2:  (hid_open_mut){+.+...}, at: [<ffffffffa0056388>]
>>>> usbhid_close+0x28/0xb0 [usbhid]
>>>> [   23.046106] irq event stamp: 3306
>>>> [   23.046109] hardirqs last  enabled at (3305): [<ffffffff8192ae32>]
>>>> _raw_spin_unlock_irq+0x32/0x60
>>>> [   23.046115] hardirqs last disabled at (3306): [<ffffffff81121017>]
>>>> del_timer_sync+0x37/0x110
>>>> [   23.046122] softirqs last  enabled at (2704): [<ffffffff818b12c9>]
>>>> local_bh_enable+0x9/0x20
>>>> [   23.046128] softirqs last disabled at (2702): [<ffffffff818b12a9>]
>>>> local_bh_disable+0x9/0x20
>>>> [   23.046136] CPU: 2 PID: 1399 Comm: acpid Not tainted
>>>> 4.3.0-rc3-3-llvmlinux-amd64 #1
>>>> [   23.046139] Hardware name: SAMSUNG ELECTRONICS CO., LTD.
>>>> 530U3BI/530U4BI/530U4BH/530U3BI/530U4BI/530U4BH, BIOS 13XK 03/28/2013
>>>> [   23.046143]  ffff8800d36ee948 0000000000000092 0000000000000000
>>>> ffff8800bbacfae8
>>>> [   23.046151]  ffffffff8149adad ffff8800bbacfb18 ffffffff810cd1ea
>>>> ffffffff81c56f0a
>>>> [   23.046158]  ffff8800c22dc400 0000000000000000 0000000000000a76
>>>> ffff8800bbacfb58
>>>> [   23.046165] Call Trace:
>>>> [   23.046172]  [<ffffffff8149adad>] dump_stack+0x7d/0xa0
>>>> [   23.046177]  [<ffffffff810cd1ea>] ___might_sleep+0x28a/0x2a0
>>>> [   23.046182]  [<ffffffff810cceef>] __might_sleep+0x4f/0xc0
>>>> [   23.046187]  [<ffffffff810afbff>] start_flush_work+0x2f/0x290
>>>> [   23.046192]  [<ffffffff810afbac>] flush_work+0x5c/0x80
>>>> [   23.046195]  [<ffffffff810afb6a>] ? flush_work+0x1a/0x80
>>>> [   23.046202]  [<ffffffff810eed0d>] ? trace_hardirqs_off+0xd/0x10
>>>> [   23.046206]  [<ffffffff810aecc8>] ? try_to_grab_pending+0x48/0x360
>>>> [   23.046211]  [<ffffffff8192ac53>] ? _raw_spin_lock_irqsave+0x73/0x80
>>>> [   23.046216]  [<ffffffff810afff9>] __cancel_work_timer+0x179/0x260
>>>> [   23.046221]  [<ffffffff8192add2>] ? _raw_spin_unlock_irqrestore+0x52/0x80
>>>> [   23.046226]  [<ffffffff81120fcd>] ? try_to_del_timer_sync+0xad/0xc0
>>>> [   23.046230]  [<ffffffff810afe78>] cancel_work_sync+0x18/0x20
>>>> [   23.046237]  [<ffffffffa00563d5>] usbhid_close+0x75/0xb0 [usbhid]
>>>> [   23.046245]  [<ffffffffa00394d1>] hidinput_close+0x31/0x40 [hid]
>>>> [   23.046251]  [<ffffffffa00394a0>] ? hidinput_open+0x40/0x40 [hid]
>>>> [   23.046256]  [<ffffffff817423b8>] input_close_device+0x48/0x70
>>>> [   23.046261]  [<ffffffff8174ac96>] evdev_release+0xd6/0xf0
>>>> [   23.046267]  [<ffffffff812728c7>] __fput+0x107/0x240
>>>> [   23.046271]  [<ffffffff81272756>] ____fput+0x16/0x20
>>>> [   23.046276]  [<ffffffff810b945c>] task_work_run+0x6c/0xe0
>>>> [   23.046282]  [<ffffffff81003aa7>] prepare_exit_to_usermode+0x117/0x120
>>>> [   23.046287]  [<ffffffff81003ce1>] syscall_return_slowpath+0x231/0x2a0
>>>> [   23.046292]  [<ffffffff8126efa5>] ? filp_close+0x65/0x90
>>>> [   23.046298]  [<ffffffff810ef1c9>] ? trace_hardirqs_on_caller+0x19/0x290
>>>> [   23.046303]  [<ffffffff81003017>] ? trace_hardirqs_on_thunk+0x17/0x19
>>>> [   23.046308]  [<ffffffff8192bb62>] int_ret_from_sys_call+0x25/0x9f
>>>>
>>>> Can you give help on how to "debug" this?
>>>>
>>>> I switched from full-dynticks to simple cpu-accounting which did not help.
>>>> But this was only a suspicion as Jiri pointed to the possibility
>>>> del_timer_sync() could have get some mis-optimization.
>>>>
>>>> So, more empty head here.
>>>>
>>>
>>> Forgot to attach dmesg-log and my kernel-config.
>>> Sorry about that.
>>>
>>
>> Time for a pause!
>>
>> Forgot to attach disassembled kernel/workqueue.o.
>>
>
> When looking at start_flush_work() in kernel/workqueue.c...
> ...I remembered the comments of Lai Jiangshan concerning the
> might_sleep() check there.
>
> I tried to move the might_sleep() line to __cancel_work_timer() as
> requested, but that did not help or narrowed down whatever.
>
> Please see [1] for more details.
>
> - Sedat -
>
> [1] http://marc.info/?l=linux-kernel&m=144184707824750&w=2

Sorry, before you dig to deeply inside this.

Jiri made a good analysis on the hid side looking at my stack trace... see [2].

- Sedat -

[2] http://marc.info/?l=linux-kernel&m=144308152407025&w=2
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