Re: [GIT PULL rcu/urgent] Fix two more 4.3 regressions

From: Sedat Dilek
Date: Sun Sep 27 2015 - 12:16:47 EST

On Sun, Sep 27, 2015 at 6:02 PM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> On Sun, Sep 27, 2015 at 5:58 PM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
>> On Sun, Sep 27, 2015 at 5:55 PM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
>>> On Sun, Sep 27, 2015 at 5:49 PM, Paul E. McKenney
>>> <paulmck@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx> 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
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