Messages in this thread | | | Date | Mon, 14 Feb 2011 19:06:09 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE_ATTACH |
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On 02/14, Oleg Nesterov wrote: > > On 02/14, Denys Vlasenko wrote: > > > > On Mon, Feb 14, 2011 at 6:39 PM, Oleg Nesterov <oleg@redhat.com> wrote: > > > On 02/14, Denys Vlasenko wrote: > > >> > > >> On Mon, Feb 14, 2011 at 4:31 PM, Oleg Nesterov <oleg@redhat.com> wrote: > > >> > On 02/13, Denys Vlasenko wrote: > > >> >> > > >> >> $ strace -tt sleep 30 > > >> >> 23:02:15.619262 execve("/bin/sleep", ["sleep", "30"], [/* 30 vars */]) = 0 > > >> >> ... > > >> >> 23:02:15.622112 nanosleep({30, 0}, NULL) = ? ERESTART_RESTARTBLOCK (To be restarted) > > >> >> 23:02:23.781165 --- SIGSTOP (Stopped (signal)) @ 0 (0) --- > > >> >> 23:02:23.781251 --- SIGSTOP (Stopped (signal)) @ 0 (0) --- > > >> >> (I forgot again why we see it twice. Another quirk I guess...) > > >> > > > >> > (this is correct, the tracee reports the signal=SIGSTOP, then > > >> > it reports it actually stopps with exit_code=SIGSTOP) > > >> > > >> Ah, I see. Is there any way debugger can distinguish between these two > > >> different stops? > > > > > > IIRC, the (only?) way to distinguish is to check last_siginfo != NULL > > > via ptrace(PTRACE_GETSIGINFO). > > > > What do you think strace needs to do when it sees second SIGSTOP > > (meaning "in theory", not "on current kernel which may be buggy")? > > > > ptrace(PTRACE_SYSCALL, $PID, 0x1, 0)? > > proably this, or even ptrace(PTRACE_SYSCALL, $PID, 0x1, SIGSTOP). > I think. > > (assuming that ptrace_resume() respects TASK_STOPPED)
Oh, but I forgot to mention... there is another problem, _any_ ptrace request when the tracee is stopped turns it into TASK_TRACED.
Oleg.
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