Messages in this thread | | | Date | Tue, 19 Mar 2013 21:19:33 +0100 | From | Oleg Nesterov <> | Subject | Re: ptracing a task from core_pattern pipe |
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On 03/18, Daniel Walker wrote: > > On Mon, Mar 18, 2013 at 06:03:02PM +0100, Oleg Nesterov wrote: > > > > > For instance, I ptrace attach from inside the corepipe_app then try > > > PTRACE_GETREGS and you get -ESRCH . > > > > Sure. PTRACE_GETREGS and (almost) any other request can only succeed > > if the tracee is TASK_TRACED! I already told you that ptrace() doesn't > > and can't work exactly because the dumper never does ptrace_stop(). > > When does ptrace_stop run ?
When the tracee stops in TASK_TRACED for debugger, after that the debugger can do ptrace(GETREGS/whatever).
> > > I'm not sure if it would accomplish what I need. I can't save the whole core, > > > and I can't get memory to save large chunks of it. > > > > Not sure I understand this part... > > The above is regarding the situation which I'm running my corepipe_app , > i.e. my system doesn't have a disk to save a core file for parsing.
Can't you process the data inplace? You do not need to save it to disk.
I understand, this is probably not very convenient, but any new kernel feature should be justified. And let me repeat, even if we add PTRACE_EVENT_COREDUMPED you won't be able to ptrace sub-threads, so this feature doesn't look very nice.
> > > Oh, I think I see what you mean. I would ptrace attach prior to the > > > thread crashing , > > > > I don't understand what "prior to the thread crashing" means... the pipe > > hanlder is spawned after the task has already initiated the coredump... > > IOW, other threads are already killed and we are ready to actually dump > > the core. > > I can't attach to the thread after it's crashed,
Daniel, you can, but:
> since I get ESRCH in > the corepipe_app for every operation,
This is another thing, and I already explained many times why this happens.
> so that suggests I'd need to attach > prior to when it crashes.
If you can attach prior to when it crashes then I do not understand why do you need the piped coredump at all. You can do everything you need after the tracee reports SEGFAULT or another sig_kernel_coredump() signal.
> > And get an event after coredump_app closes the pipe. Assuming that > > you use PTRACE_SEIZE(PTRACE_O_CORE_DUMPED) rather that PTRACE_ATTACH. > > And assuming you do this before you close the pipe, otherwise it can > > exit before you do PTRACE_SEIZE. > > So corepipe_app would PTRACE_SEIZE then close the pipe but continue running ?
Well, yes... But I am not sure I understand the question...
What this "but continue running" means? Of course corepipe_app can run after it closes the pipe.
Daniel, I feel you misunderstand something (or perhaps it is me), but I can't understand what exactly you do not understand, sorry ;) I will be happy to help if you ask the more "explicit" questions.
Oleg.
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