[Click] Multithreading bug

[Eddie Kohler]

Hi Beyers,

Any word on if the suggested change helped?

E


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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