[SCM] strace branch, master, updated. v4.5.20-103-g7b6847b

[Oleg Nesterov]

On 03/14, Denys Vlasenko wrote:
>
> On Fri, 2011-03-11 at 23:53 +0300, Dmitry V. Levin wrote:
> > On Thu, Mar 10, 2011 at 12:26:08PM +0100, Denys Vlasenko wrote:
> > > +				in_job_control_stop = 0;
> > > +				if (WSTOPSIG(status) == SIGSTOP ||
> > > +				    WSTOPSIG(status) == SIGTSTP ||
> > > +				    WSTOPSIG(status) == SIGTTIN ||
> > > +				    WSTOPSIG(status) == SIGTTOU) {
> > > +					/*
> > > +					 * PTRACE_GETSIGINFO fails if this is
> > > +					 * genuine *stop* notification,
> > > +					 * not *signal* notification
> > > +					 */
> > > +					siginfo_t si;
> > > +					if (ptrace(PTRACE_GETSIGINFO, pid,
> > > +						    0, &si) != 0)
> > > +						in_job_control_stop = 1;
> > > +				}
> > >  				printleader(tcp);
> > > -				tprintf("--- %s (%s) @ %lx (%lx) ---",
> > > +				tprintf(in_job_control_stop
> > > +					? "--- stopped by %s ---"
> > > +					: "--- %s (%s) @ %lx (%lx) ---",
> >
> > In addition to what I've already written in this thread, I want to point
> > out that, unfortunately, this "stopped by" wording contradicts with
> > reality.  The tracee is just trapped, and there are no means to make
> > it really stopped without detaching.

No, it is not trapped (although this depends on how you define this).
It is really stopped.

Just in case, and it is 'T (stopped)' not 'traced' if this matters, but
we are going to change this this detail.

> During those discussions, several people, including me,
> were again puzzled by "double SIGSTOP" thing in strace.
>
> I think that making strace explicitly tell the user
> how exactly the second SIGSTOP is different from first one
> is beneficial. Yes, until kernel work is finished, straced
> process won't actually stop, but at least strace messages
> will be a bit less obscure.

I agree. Even if I know what the kernel/strace do, the current output
looks confusing to me. And do not forget the multi-threading case.
I didn't verify this, but I guess in this case strace -f reports
SIGSTOP for every thread, this is simply not true. Only one thread
recieves SIGSTOP and then stops, all other thread simply stop.

Oleg.