Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 18 Dec 2006 20:05:35 +0100 (CET) | From | Nicholas Mc Guire <> | Subject | problem with signal delivery SIGCHLD |
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Hi !
I have a phenomena that I don't quite understand. gdbserver forks and after setting ptrace (PTRACE_TRACEME, 0, 0, 0); it then execv (program, allargs); when this child process hits ptrace_stoped (breakpoint it does the following in kernel space:
pid 1242 = child process pid 1241 = gdbserver pid 0 = kernel pid -1 = interrupt pid 1 559 5 1242 ptrace_stop 3 6 2 1242 | do_notify_parent_cldstop 4 3 2 1242 | | __group_send_sig_info 5 1 1 1242 | | | handle_stop_signal 7 0 0 1242 | | | sig_ignored 8 1 0 1242 | | __wake_up_sync 8 1 1 1242 | | | __wake_up_common 10 547 541 1242 | schedule 10 2 2 1242 | | profile_hit 13 1 1 1242 | | sched_clock 15 1 0 1242 | | deactivate_task 15 1 1 1242 | | | dequeue_task 19 2 2 0 | | __switch_to ----------- !!!! start -------------- 24 574 574 0 default_idle ----------- $$$$ end ---------------- ----------- //// start -------------- 780 41 12 0 do_IRQ 780 29 2 -1 / __do_IRQ ... 807 2 2 -1 / / / enable_8259A_irq ----------- //// end ---------------- ----------- {{{{ start -------------- 810 11 0 0 do_softirq ... 820 0 0 -1 { { { preempt_schedule ----------- {{{{ end ---------------- ----------- %%%% start -------------- 822 358 1 0 preempt_schedule_irq ... 827 1 1 1241 % % __switch_to ----------- %%%% end ---------------- 829 1 1 1241 ( ( ( del_timer ----------- (((( end ---------------- ----------- ]]]] start -------------- 837 8 2 1241 sys_waitpid
So basically child signals -> delayed to next tick -> parent wakes up.
now what I don't understand is why does it not schedule the parent ? in fact the traces show that on an idle system the parent will not be scheduled until the next tick.
I don't want to post the full traces as they are very lengthy - but if someone could point me in what direction to search to find out why this delay between the child process signaling and the parent breaking out of waitpid it would be helpfull - the background is that we implemented GDB tracepoints but they only work properly on highly loaded systems (the parent gets scheduled fast then and the tracepoint is processed "fast" but on an idle system it is simply not usabel as you get almost deterministic 10ms between the child process signaling and the parent waking up...
Is this delay on sigchild expected behavior ?
any ideas ?
thx ! hofrat
ps.: if anybody is intersted in the detailed logs see http://dslab.lzu.edu.cn/~hofrat/sigchld_problem.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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