[Click] [PATCH 2/2] Task: Kill process_pending dead lock
Eddie Kohler
kohler at cs.ucla.edu
Mon Nov 3 16:59:44 EST 2008
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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