[Click] [PATCH 2/2] Task: Kill process_pending dead lock
Joonwoo Park
joonwpark81 at gmail.com
Tue Sep 16 13:26:32 EDT 2008
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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