[Click] [PATCH 2/2] Task: Kill process_pending dead lock
Joonwoo Park
joonwpark81 at gmail.com
Mon Nov 3 17:29:04 EST 2008
Hello Eddie,
Thank you for your reviewing. I cannot take a look at the code, I'll
check my patch soon again as soon as I have a chance.
I am not using click for work nowadays. So it's pretty hard to spend
enough time for it.
Anyhow, I have been turning on the kassert. However I couldn't see
assertion failure (both before & after patching)
It it make sense?
Thanks,
Joonwoo
On Mon, Nov 3, 2008 at 2:59 PM, Eddie Kohler <kohler at cs.ucla.edu> wrote:
> Joonwoo,
>
> I don't think this patch has any affect on the correctness of the code. It
> just slows things down.
>
> There are also bugs in the patch, including setting _task_blocker_owner in
> RouterThread::attempt_lock_tasks but not resetting it if the attempt fails.
>
> Have you run after having configured with --enable-kassert? If so, do you
> see any assertions? If not, could you please?
>
> I'd like to track this down, but this patch is not the way.
> Eddie
>
>
> Joonwoo Park wrote:
>>
>> Hello Eddie,
>>
>> I tried to fix task blocker to support nested locking and attached a
>> patch.
>> Can you please take a look at this? I've tested minimally.
>>
>> Thanks!
>> Joonwoo
>>
>> On Tue, Sep 16, 2008 at 9:26 AM, Joonwoo Park <joonwpark81 at gmail.com>
>> wrote:
>>>
>>> I am folking 3 threads.
>>>
>>> Joonwoo
>>>
>>> 2008/9/16 Eddie Kohler <kohler at cs.ucla.edu>:
>>>>
>>>> And how many threads?
>>>>
>>>> Eddie
>>>>
>>>>
>>>> Joonwoo Park wrote:
>>>>>
>>>>> Hi Eddie,
>>>>>
>>>>> I guess so that you intended to they are recursive. :-)
>>>>> Here is the config can cause lock up without device elements.
>>>>>
>>>>> ----
>>>>> s0::RatedSource(DATASIZE 128) -> EtherEncap(0x0800, FF:FF:FF:FF:FF:FF,
>>>>> FF:FF:FF:FF:FF:FF) -> Discard
>>>>> s1::InfiniteSource(DATASIZE 128) -> EtherEncap(0x0800,
>>>>> FF:FF:FF:FF:FF:FF, FF:FF:FF:FF:FF:FF) -> Discard
>>>>>
>>>>> sched::BalancedThreadSched(100);
>>>>> ----
>>>>>
>>>>> Thanks!
>>>>> Joonwoo
>>>>>
>>>>> 2008/9/16 Eddie Kohler <kohler at cs.ucla.edu>:
>>>>>>
>>>>>> Hi Joonwoo,
>>>>>>
>>>>>> I intended block_tasks() and driver_lock_tasks() to be recursive. I
>>>>>> could
>>>>>> certainly have failed! Can you tell me more about the configuration
>>>>>> you're
>>>>>> running? Can you cause a soft lockup even without device elements
>>>>>> (such
>>>>>> as
>>>>>> with InfiniteSources)?
>>>>>>
>>>>>> Eddie
>>>>>>
>>>>>>
>>>>>> Joonwoo Park wrote:
>>>>>>>
>>>>>>> Hi Eddie,
>>>>>>>
>>>>>>> I agree with your blocking task execution as a solution.
>>>>>>> However I got a following soft lock up problem with your patch.
>>>>>>> With a quick review, it's seems to block_tasks() and driver_tasks()
>>>>>>> doesn't support recursive lock. (please correct me if I am wrong)
>>>>>>> So when BalancedThreadSched's run_timer try to lock the tasks, it
>>>>>>> looks like goes hang.
>>>>>>>
>>>>>>> Here is my oops message and gdb output. I used my 2.6.24 patched
>>>>>>> kernel. I'm sorry for that.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Joonwoo
>>>>>>>
>>>>>>> joonwpark at joonwpark-desktop-64:~/SRC5/click/linuxmodule$ BUG: soft
>>>>>>> lockup - CPU#0 stuck for 11s! [kclick:3116]
>>>>>>> SysRq : Changing Loglevel
>>>>>>> Loglevel set to 9
>>>>>>> BUG: soft lockup - CPU#0 stuck for 11s! [kclick:3116]
>>>>>>> CPU 0:
>>>>>>> Modules linked in: click proclikefs e1000 iptable_filter ip_tables
>>>>>>> x_tables parport_pc lp parport ipv6 floppy pcspkr forcedeth ext3 jbd
>>>>>>> Pid: 3116, comm: kclick Not tainted 2.6.24.7-joonwpark #3
>>>>>>> RIP: 0010:[<ffffffff881f818a>] [<ffffffff881f818a>]
>>>>>>> :click:_ZN19BalancedThreadSched9run_timerEP5Timer+0x58a/0x630
>>>>>>> RSP: 0018:ffff8100370d7d30 EFLAGS: 00000286
>>>>>>> RAX: ffff8100370d4000 RBX: ffff8100370d7dc0 RCX: ffff810037892430
>>>>>>> RDX: 00000000ffffffff RSI: ffff81003792fcd0 RDI: ffff81003792fc60
>>>>>>> RBP: ffffffff806b7b10 R08: 0000000000000000 R09: 0000000000000000
>>>>>>> R10: 0000000000000000 R11: 0000000000000005 R12: 0000000000000001
>>>>>>> R13: ffff810080643000 R14: ffff8100370d6000 R15: 0000000000000001
>>>>>>> FS: 00002acdb07f76e0(0000) GS:ffffffff806ae000(0000)
>>>>>>> knlGS:0000000000000000
>>>>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>>>>> CR2: 00000000007ad008 CR3: 000000006bdf2000 CR4: 00000000000006e0
>>>>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>>>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>>>>>>
>>>>>>> Call Trace:
>>>>>>> [<ffffffff88166803>] :click:_Z12element_hookP5TimerPv+0x13/0x20
>>>>>>> [<ffffffff8818ebc8>] :click:_ZN6Master10run_timersEv+0x178/0x320
>>>>>>> [<ffffffff88183349>] :click:_ZN12RouterThread6driverEv+0x5b9/0x6f0
>>>>>>> [<ffffffff881f9ffe>] :click:_Z11click_schedPv+0xfe/0x260
>>>>>>> [<ffffffff804e4fef>] _spin_unlock_irq+0x2b/0x30
>>>>>>> [<ffffffff8022e0b6>] finish_task_switch+0x57/0x94
>>>>>>> [<ffffffff8020cfe8>] child_rip+0xa/0x12
>>>>>>> [<ffffffff8022e0b6>] finish_task_switch+0x57/0x94
>>>>>>> [<ffffffff8020c6ff>] restore_args+0x0/0x30
>>>>>>> [<ffffffff881f9f00>] :click:_Z11click_schedPv+0x0/0x260
>>>>>>> [<ffffffff8020cfde>] child_rip+0x0/0x12
>>>>>>>
>>>>>>>
>>>>>>> joonwpark at joonwpark-desktop-64:~/SRC5/click/linuxmodule$ gdb click.ko
>>>>>>> GNU gdb 6.8-debian
>>>>>>> Copyright (C) 2008 Free Software Foundation, Inc.
>>>>>>> License GPLv3+: GNU GPL version 3 or later
>>>>>>> <http://gnu.org/licenses/gpl.html>
>>>>>>> This is free software: you are free to change and redistribute it.
>>>>>>> There is NO WARRANTY, to the extent permitted by law. Type "show
>>>>>>> copying"
>>>>>>> and "show warranty" for details.
>>>>>>> This GDB was configured as "x86_64-linux-gnu"...
>>>>>>> info line *(gdb) info line
>>>>>>> *_ZN19BalancedThreadSched9run_timerEP5Timer+0x58a
>>>>>>> Line 311 of
>>>>>>>
>>>>>>>
>>>>>>> "/home/joonwpark/SRC5/click/linuxmodule/../include/click/routerthread.hh"
>>>>>>> starts at address 0x9c1ba
>>>>>>> <_ZN19BalancedThreadSched9run_timerEP5Timer+1418>
>>>>>>> and ends at 0x9c1be
>>>>>>> <_ZN19BalancedThreadSched9run_timerEP5Timer+1422>.
>>>>>>> (gdb) l
>>>>>>>
>>>>>>>
>>>>>>> "/home/joonwpark/SRC5/click/linuxmodule/../include/click/routerthread.hh:311
>>>>>>> 306 assert(!current_thread_is_running());
>>>>>>> 307 if (!scheduled)
>>>>>>> 308 ++_task_blocker_waiting;
>>>>>>> 309 while (1) {
>>>>>>> 310 int32_t blocker = _task_blocker.value();
>>>>>>> 311 if (blocker >= 0
>>>>>>> 312 && _task_blocker.compare_and_swap(blocker,
>>>>>>> blocker +
>>>>>>> 1))
>>>>>>> 313 break;
>>>>>>> 314 if (nice) {
>>>>>>> 315 #if CLICK_LINUXMODULE
>>>>>>> (gdb)
>>>>>>>
>>>>>>>
>>>>>>> 2008/9/15 Eddie Kohler <kohler at cs.ucla.edu>:
>>>>>>>>
>>>>>>>> Joonwoo,
>>>>>>>>
>>>>>>>>> I took look into this lock up issue and I think I found something.
>>>>>>>>>
>>>>>>>>> RoutherThread::driver() calls run_tasks() with locked tasks.
>>>>>>>>> But after calling run_tasks(), current processor can be changed
>>>>>>>>> since
>>>>>>>>> schedule() might be called (eg. ScheduleLinux element)
>>>>>>>>> So I think that's problem. How do you think?
>>>>>>>>
>>>>>>>> I totally agree that this could be a problem.
>>>>>>>>
>>>>>>>> It looks like EXCLUSIVE handlers never really worked before. :(
>>>>>>>>
>>>>>>>> So my current analysis is this. It is not appropriate for a thread
>>>>>>>> to
>>>>>>>> call
>>>>>>>> blocking functions and/or schedule() when that thread has prevented
>>>>>>>> preemption via get_cpu(). My prior patches prevented preemption.
>>>>>>>>
>>>>>>>> The solution is to separate "locking the task list" from "blocking
>>>>>>>> task
>>>>>>>> execution." Clickfs, when executing an exclusive handler, "blocks
>>>>>>>> task
>>>>>>>> execution." A thread that wants to examine the task list "locks"
>>>>>>>> the
>>>>>>>> list.
>>>>>>>>
>>>>>>>> This commit:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> http://www.read.cs.ucla.edu/gitweb?p=click;a=commit;h=ede0c6b0a1cface05e8d8e2e3496ee7fcd5ee143
>>>>>>>> introduces separate APIs for locking the list and blocking task
>>>>>>>> execution.
>>>>>>>> Exclusive handlers block task execution, but do not lock the task
>>>>>>>> list.
>>>>>>>> I
>>>>>>>> believe that task execution, in this patch, does not prevent
>>>>>>>> preemption.
>>>>>>>> I
>>>>>>>> believe the locking works out too. User-level multithreading tests
>>>>>>>> appear
>>>>>>>> OK.
>>>>>>>>
>>>>>>>> Any willing stresstesters? Pretty please? :)
>>>>>>>>
>>>>>>>> Eddie
>>>>>>>>
>
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