On 01/05, Martin Schwidefsky wrote: > > On Mon, 4 Jan 2010 13:11:47 -0800 (PST) > Roland McGrath <roland@xxxxxxxxxx> wrote: > > > > This probably means that copy_process()->user_disable_single_step() > > > is not enough to clear the "this task wants single-stepping" copied > > > from parent. > > > > I would suspect s390's TIF_SINGLE_STEP flag here. That flag means "a > > single-step trap occurred". This is what causes do_single_step to be > > called before returning to user mode, rather than the machine trap doing it > > directly as is done in the other arch implementations. > > Just my thinking as well. Oh, I am not sure. But I don't understand TIF_SINGLE_STEP on s390, absolutely. For example, why do_signal() sets TIF_SINGLE_STEP? Why can't we do --- a/arch/s390/kernel/signal.c +++ b/arch/s390/kernel/signal.c @@ -500,18 +500,10 @@ void do_signal(struct pt_regs *regs) clear_thread_flag(TIF_RESTORE_SIGMASK); /* - * If we would have taken a single-step trap - * for a normal instruction, act like we took - * one for the handler setup. - */ - if (current->thread.per_info.single_step) - set_thread_flag(TIF_SINGLE_STEP); - - /* * Let tracing know that we've done the handler setup. */ tracehook_signal_handler(signr, &info, &ka, regs, - test_thread_flag(TIF_SINGLE_STEP)); + current->thread.per_info.single_step); } return; } ? Apart from arch/s390/signal.c, TIF_SINGLE_STEP is used by entry.S but I don't understand this asm at all. Anyway. I modified the debugging patch a bit: --- K/arch/s390/kernel/traps.c~ 2009-12-22 10:41:52.909174198 -0500 +++ K/arch/s390/kernel/traps.c 2010-01-05 09:49:19.541792379 -0500 @@ -384,6 +384,8 @@ void __kprobes do_single_step(struct pt_ } if (tracehook_consider_fatal_signal(current, SIGTRAP)) force_sig(SIGTRAP, current); + else + printk("XXX: %d %d\n", current->pid, test_thread_flag(TIF_SINGLE_STEP)); } static void default_trap_handler(struct pt_regs * regs, long interruption_code) ------------------------------------------------------------------------------- Now, when I run this test-case #include <stdio.h> #include <unistd.h> #include <signal.h> #include <sys/ptrace.h> #include <sys/wait.h> #include <assert.h> int main(void) { int pid, status; if (!(pid = fork())) { assert(ptrace(PTRACE_TRACEME) == 0); kill(getpid(), SIGSTOP); if (!fork()) return 43; wait(&status); return WEXITSTATUS(status); } for (;;) { assert(pid == wait(&status)); if (WIFEXITED(status)) break; assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0); } assert(WEXITSTATUS(status) == 43); return 0; } dmesg shows 799 lines of XXX: 2389 0 The kernel is 2.6.32.2 + utrace, but CONFIG_UTRACE is not set. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html