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 > _______________________________________________ > click mailing list > [email protected] > https://amsterdam.lcs.mit.edu/mailman/listinfo/click _______________________________________________ click mailing list [email protected] https://amsterdam.lcs.mit.edu/mailman/listinfo/click
