[Click] [PATCH 2/2] Task: Kill process_pending dead lock
Joonwoo Park
joonwpark81 at gmail.com
Tue Sep 16 13:07:19 EDT 2008
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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