Messages in this thread | | | Date | Mon, 27 Aug 2012 20:56:49 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [RFC 5/5 v2] uprobes: add global breakpoints |
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On 08/22/2012 03:48 PM, Oleg Nesterov wrote: > On 08/21, Sebastian Andrzej Siewior wrote: >> >> This patch adds the ability to hold the program once this point has been >> passed and the user may attach to the program via ptrace. > > Sorry Sebastian, I didn't even try to read the patch ;) Fortunately I am > not maintainer, I can only reapeat that you do not need to convince me.
At least for the ptrace part I would prefer to have your blessing instead something that seems to work but is wrong.
>> Oleg: The change in ptrace_attach() is still as it was. I tried to >> address Peter concern here. >> Now what options do I have here: >> - not putting the task in TASK_TRACED but simply halt. This would work >> without a change to ptrace_attach() but the task continues on any >> signal. So a signal friendly task would continue and not notice a >> thing. > > TASK_KILLABLE
That would help but would require a change in ptrace_attach() or something in gdb/strace/…
One thing I just noticed: If I don't register a handler for SIGUSR1 and send one to the application while it is in TASK_KILLABLE then the signal gets delivered. If I register a signal handler for it than it gets blocked and delivered once I resume the task. Shouldn't it get blocked even if I don't register a handler for it?
>> - putting the TASK_TRACED > > This is simply wrong, in many ways. > > For example, what if the probed task is already ptraced? Or debugger > attaches via PTRACE_SEIZE? How can debugger know it is stopped? > uprobe_wait_traced() goes to sleep in TASK_TRACED without notification. > And it does not set ->exit_code, this means do_wait() won't work. > And note ptrace_stop()->recalc_sigpending_tsk().
Okay, okay. It looks like it is better to stick with TASK_KILLABLE instead of fixing the issues you pointed out.
>> --- a/kernel/events/uprobes.c >> +++ b/kernel/events/uprobes.c >> @@ -1513,7 +1513,16 @@ static void handle_swbp(struct pt_regs *regs) >> goto cleanup_ret; >> } >> utask->active_uprobe = uprobe; >> - handler_chain(uprobe, regs); >> + if (utask->skip_handler) >> + utask->skip_handler = 0; >> + else >> + handler_chain(uprobe, regs); >> + >> + if (utask->state == UTASK_TRACE_WOKEUP_TRACED) { >> + send_sig(SIGTRAP, current, 0); >> + utask->skip_handler = 1; >> + goto cleanup_ret; >> + } >> if (uprobe->flags& UPROBE_SKIP_SSTEP&& can_skip_sstep(uprobe, regs)) >> goto cleanup_ret; >> >> @@ -1528,7 +1537,7 @@ cleanup_ret: >> utask->active_uprobe = NULL; >> utask->state = UTASK_RUNNING; >> } >> - if (!(uprobe->flags& UPROBE_SKIP_SSTEP)) >> + if (!(uprobe->flags& UPROBE_SKIP_SSTEP) || utask->skip_handler) > > Am I understand correctly? > > If it was woken by PTRACE_ATTACH we set utask->skip_handler = 1 and > re-execute the instruction (yes, SIGTRAP, but this doesn't matter). > When the task hits this bp again we skip handler_chain() because it > was already reported. > > Yes? If yes, I don't think this can work. Suppose that the task > dequeues a signal before it returns to the usermode to re-execute > and enters the signal handler which can hit another uprobe.
ach, those signals make everything complicated. I though signals are blocked until the single step is done but my test just showed my something different. Okay, what now? A simple nested struct uprobe_task and struct uprobe? Blocking signals isn't probably a good idea.
> And this can race with uprobe_register() afaics.
> Oleg.
Sebastian -- 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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