[Click] Multithreading bug

[Beyers Cronje]

Perfect, that works for me.

On Wed, May 11, 2011 at 3:25 PM, Eddie Kohler <kohler at cs.ucla.edu> wrote:

> Good catch!  This is a bug in Socket.  The fast_reschedule() method should
> only be called when an element is truly being run from the scheduler.  (I
> guess the documentation is a bit ambiguous.)  It is safe to call
> reschedule() from anywhere; I would suggest just changing Socket::run_task()
> to call reschedule().
>
> Eddie
>
>
>
> On 5/11/11 6:09 AM, Beyers Cronje wrote:
>
>> Hi guys,
>>
>> I seem to have come across a userlevel click multithreading bug. In short,
>> when running multiple threads in userlevel click with Socket element it
>> can
>> happen that two separate threads end up in fast_reschedule() at the same
>> time causing click to crash at the following line: task.hh:558   while (n
>> !=
>> _thread&&  !PASS_GT(n->_pass, _pass))
>>
>> One thread runs Socket::run_task() via standard task scheduling, while the
>> second thread call Socket::run_task() via Socket::selected() scheduling.
>> This will obviously affect any other element that calls run_task() via
>> selected().
>>
>> Eddie, Cliff, should this issue be addressed inside Socket? Or should we
>> look at how RouterThread handles locking with regards to task and select
>> scheduling?
>>
>> Below the stack traces: 7 threads, with thread 1 and 6 being the culprits.
>>
>> (gdb) info threads
>>   7 Thread 23122  0x000000392cedcee3 in select () from /lib64/libc.so.6
>>   6 Thread 23121  0x000000000054ce1b in fast_reschedule (this=0x14571e0)
>> at
>> ../include/click/task.hh:558
>>   5 Thread 23125  0x000000000058471b in RouterThread::driver
>> (this=0x1445bb0) at ../lib/routerthread.cc:565
>>   4 Thread 23120  FromDAG::run_task (this=0x1456990) at fromdag.cc:157
>>   3 Thread 23112  0x0000000000560305 in Packet::~Packet (this=0x14b22f0,
>> __in_chrg=<value optimized out>) at ../lib/packet.cc:181
>>   2 Thread 23124  0x00000000005844b0 in RouterThread::driver
>> (this=0x1445af0) at ../lib/routerthread.cc:594
>> * 1 Thread 23123  0x000000000054ce1b in fast_reschedule (this=0x14571e0)
>> at
>> ../include/click/task.hh:558
>>
>> (gdb) thread 1
>> [Switching to thread 1 (Thread 23123)]#0  0x000000000054ce1b in
>> fast_reschedule (this=0x14571e0) at ../include/click/task.hh:558
>> 558             while (n != _thread&&  !PASS_GT(n->_pass, _pass))
>> (gdb) bt
>> #0  0x000000000054ce1b in fast_reschedule (this=0x14571e0) at
>> ../include/click/task.hh:558
>> #1  Socket::run_task (this=0x14571e0) at
>> ../elements/userlevel/socket.cc:524
>> #2  0x00000000005845d6 in fire (this=0x1445a30) at
>> ../include/click/task.hh:612
>> #3  run_tasks (this=0x1445a30) at ../lib/routerthread.cc:405
>> #4  RouterThread::driver (this=0x1445a30) at ../lib/routerthread.cc:594
>> #5  0x0000000000556e39 in thread_driver (user_data=<value optimized out>)
>> at
>> click.cc:414
>> #6  0x000000392d206d5b in start_thread () from /lib64/libpthread.so.0
>> #7  0x000000392cee4aad in clone () from /lib64/libc.so.6
>>
>> (gdb) thread 6
>> [Switching to thread 6 (Thread 23121)]#0  0x000000000054ce1b in
>> fast_reschedule (this=0x14571e0) at ../include/click/task.hh:558
>> 558             while (n != _thread&&  !PASS_GT(n->_pass, _pass))
>> (gdb) bt
>> #0  0x000000000054ce1b in fast_reschedule (this=0x14571e0) at
>> ../include/click/task.hh:558
>> #1  Socket::run_task (this=0x14571e0) at
>> ../elements/userlevel/socket.cc:524
>> #2  0x000000000054c2cf in Socket::selected (this=0x14571e0, fd=<value
>> optimized out>) at ../elements/userlevel/socket.cc:417
>> #3  0x0000000000592856 in call_selected (this=0x1444c50, thread=<value
>> optimized out>, more_tasks=<value optimized out>) at ../lib/master.cc:732
>> #4  Master::run_selects_poll (this=0x1444c50, thread=<value optimized
>> out>,
>> more_tasks=<value optimized out>) at ../lib/master.cc:889
>> #5  0x0000000000592f34 in Master::run_selects (this=0x1444c50,
>> thread=0x14458b0) at ../lib/master.cc:1050
>> #6  0x00000000005847d7 in run_os (this=0x14458b0) at
>> ../lib/routerthread.cc:442
>> #7  RouterThread::driver (this=0x14458b0) at ../lib/routerthread.cc:562
>> #8  0x0000000000556e39 in thread_driver (user_data=<value optimized out>)
>> at
>> click.cc:414
>> #9  0x000000392d206d5b in start_thread () from /lib64/libpthread.so.0
>> #10 0x000000392cee4aad in clone () from /lib64/libc.so.6
>>
>>
>> Beyers
>> _______________________________________________
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>> click at amsterdam.lcs.mit.edu
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>>
>