[Click] [PATCH 2/2] Task: Kill process_pending dead lock
Eddie Kohler
kohler at cs.ucla.edu
Tue Nov 4 11:12:46 EST 2008
Joonwoo,
Multiple routerthreads will NEVER call driver_lock_tasks() on THE SAME
ROUTERTHREAD OBJECT at the same time.
Each routerthread has exactly ONE kernel thread, and only that kernel thread
ever calls driver_lock_tasks().
Does this help?
Eddie
Joonwoo Park wrote:
> Hi Eddie,
>
> Thanks for your work and I am very happy to help click project even
> though it's just a little bit.
>
> I have a quick question about your work. I think it could fix the
> problem between block_tasks() and others.
> However still it seems to have a problem between driver_lock_tasks()
> and driver_lock_tasks().
>
> What I'm concerning is like this:
> access clickfs
> multiple _task_blocker_waitings became 1
> schedule
> multiple routerthreads call driver_lock_tasks() at the same time
> dead lock at code : while (!_task_blocker.compare_and_swap(0, -1))
>
> How do you think?
> Please correct me if I'm wrong and I'm sorry that I can't be help a lot.
>
> Thanks,
> Joonwoo
>
> On Mon, Nov 3, 2008 at 6:32 PM, Eddie Kohler <kohler at cs.ucla.edu> wrote:
>> Hi Joonwoo,
>>
>> I appreciate all your work. Thanks for the time you have spent!
>>
>> After some poking around and a bunch of rebooting, I have a different
>> analysis of the problem, and have checked in a patch. It is here:
>>
>> http://www.read.cs.ucla.edu/gitweb?p=click;a=commit;h=7312a95decddc7c4f5043d29d622dc9efb99a547
>>
>> Does this make sense? And if and when you get a chance, does it work for
>> you?
>>
>> Eddie
>>
>>
>> Joonwoo Park wrote:
>>> 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
>>>>>>>>>>>
More information about the click
mailing list