linux-kernel - Re: [Linux v4.2] workqueue: llvmlinux: acpid: BUG: sleeping function called from invalid context at kernel/workqueue.c:2680

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Date:	Fri, 25 Sep 2015 08:43:54 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Jiri Kosina <jikos@...nel.org>
Cc:	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [Linux v4.2] workqueue: llvmlinux: acpid: BUG: sleeping function
 called from invalid context at kernel/workqueue.c:2680

On Thu, Sep 24, 2015 at 10:21 AM, Jiri Kosina <jikos@...nel.org> wrote:
> On Thu, 24 Sep 2015, Sedat Dilek wrote:
>
>> >> > >> [   24.705767]  [<ffffffff8149287d>] dump_stack+0x7d/0xa0
>> >> > >> [   24.705774]  [<ffffffff810cbf7a>] ___might_sleep+0x28a/0x2a0
>> >> > >> [   24.705779]  [<ffffffff810cbc7f>] __might_sleep+0x4f/0xc0
>> >> > >> [   24.705784]  [<ffffffff810ae8ff>] start_flush_work+0x2f/0x290
>> >> > >> [   24.705789]  [<ffffffff810ae8ac>] flush_work+0x5c/0x80
>> >> > >> [   24.705792]  [<ffffffff810ae86a>] ? flush_work+0x1a/0x80
>> >> > >> [   24.705799]  [<ffffffff810eddcd>] ? trace_hardirqs_off+0xd/0x10
>> >> > >> [   24.705804]  [<ffffffff810ad938>] ? try_to_grab_pending+0x48/0x360
>> >> > >> [   24.705810]  [<ffffffff81917e13>] ? _raw_spin_lock_irqsave+0x73/0x80
>> >> > >> [   24.705814]  [<ffffffff810aecf9>] __cancel_work_timer+0x179/0x260
>> >>
>> >> This one is even more strange. It says that flush_work() is being called
>> >> from __cancel_work_timer() with IRQs disabled, but flags are explicitly
>> >> restored just one statement before that, and usbhid_close() explicitly
>> >> calls cancel_work_sync() after unconditionally enabling interrupts.
>> >>
>> >> So I am not able to make any sense of either of the traces really.
>> >>
>> >> Are you seeing this with the same .config with GCC-compiled kernel as
>> >> well?
>> >
>> > Actually could you please provide disassembly of your
>> > __cancel_work_timer()?
>> >
>>
>> Disassembly of which file - corresponding workqueue or hid file?
>
>         make kernel/workqueue.o
>         objdump -Dr kernel/workqueue.o
>
> and copy/paste output for __cancel_work_timer function.
>
>> > One explanation would be LLVM not considering local_irq_restore() a
>> > compiler memory barrier, but I am pretty sure it'll expose much more
>> > breakage if that'd be the case.
>>
>> Can you point me where I can find more informations about "compiler
>> memory barrier" or explain in a few words if possible?
>
> If compiler would not take "memory" clobber (while disabling IRQs) as a
> reordering barrier, it wouldn't see any data dependency between
> local_irq_restore(flags) and flush_work(data) and could reorder them,
> resulting in flush_work() being called with IRQs disabled.
>

BTW, is membarrier_test helpful in this case?

I asked parallelly on LTP ML is there exists something similiar.

- Sedat -

[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/membarrier
[2] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/tools/testing/selftests/membarrier/membarrier_test.c
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