From: Oleg Nesterov <oleg@redhat.com>
To: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Tejun Heo <tj@kernel.org>,
roland@redhat.com, linux-kernel@vger.kernel.org,
torvalds@linux-foundation.org, akpm@linux-foundation.org
Subject: Re: [PATCHSET RFC] ptrace,signal: clean transition between STOPPED and TRACED
Date: Thu, 13 Jan 2011 16:51:20 +0100 [thread overview]
Message-ID: <20110113155120.GA31691@redhat.com> (raw)
In-Reply-To: <20110112214350.GC13830@host1.dyn.jankratochvil.net>
On 01/12, Jan Kratochvil wrote:
>
> FSF GDB for `T (stopped)' processes currently does:
> PTRACE_ATTACH
> check /proc/%d/status for `T (stopped)' (by GDB's pid_is_stopped)
> if found then kill (PID, SIGSTOP) && ptrace (PTRACE_CONT, PID, 0, 0).
> waitpid (pid, &status, 0) - so that this one does not get stuck if the stop
> event was already eaten out before.
>
> If the `T (stopped)' will now always FAIL then at leat the waitpid then should
> never get stuck.
I think it won't stuck. With this change the tracee always goes from
TASK_STOPPED to TASK_TRACED with the correct (and nonzero) stop code.
Btw, this should fix the case when ->exit_code was already consumed
by the previous debugger.
> FSF gdbserver --multi does PTRACE_ATTACH followed by waitpid (WNOHANG) and it
> fails if it returns ECHILD on the first try.
Not sure I understand... With or without this change waitpid()
shouldn't return ECHILD. But (again, with or without this change)
it can return 0 due to WNOHANG.
> ptrace(PTRACE_ATTACH, 22049, 0, 0) = 0
> wait4(-1, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSTOP}], WNOHANG, NULL) = 22049
>
> It may be also a gdbserver bug, though.
I do not know if this matters or not, but just in case...
gdb shouldn't assume the tracee will report SIGSTOP after attach.
Yes, PTRACE_ATTACH sends this signal implicitly, but the tracee can
dequeue and report another pending signal before SIGSTOP.
Oleg.
next prev parent reply other threads:[~2011-01-13 16:00 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-24 14:00 [PATCHSET RFC] ptrace,signal: clean transition between STOPPED and TRACED Tejun Heo
2010-12-24 14:00 ` [PATCH 1/7] clone: kill CLONE_STOPPED Tejun Heo
2011-01-17 22:17 ` Roland McGrath
2011-01-27 13:13 ` Tejun Heo
2010-12-24 14:00 ` [PATCH 2/7] ptrace: add @why to ptrace_stop() Tejun Heo
2010-12-24 14:00 ` [PATCH 3/7] signal: fix premature completion of group stop when interfered by ptrace Tejun Heo
2010-12-24 14:00 ` [PATCH 4/7] signal: use GROUP_STOP_PENDING to stop once for a single group stop Tejun Heo
2010-12-24 14:00 ` [PATCH 5/7] ptrace: participate in group stop from ptrace_stop() iff the task is trapping for " Tejun Heo
2010-12-24 14:00 ` [PATCH 6/7] ptrace: make do_signal_stop() use ptrace_stop() if the task is being ptraced Tejun Heo
2010-12-24 14:00 ` [PATCH 7/7] ptrace: clean transitions between TASK_STOPPED and TRACED Tejun Heo
2011-01-05 16:35 ` Oleg Nesterov
2011-01-09 22:05 ` Tejun Heo
2011-01-13 16:03 ` Jan Kratochvil
2011-01-12 13:23 ` [PATCHSET RFC] ptrace,signal: clean transition between STOPPED " Tejun Heo
2011-01-12 18:10 ` Roland McGrath
2011-01-12 21:43 ` Jan Kratochvil
2011-01-13 15:05 ` Tejun Heo
2011-01-13 15:51 ` Oleg Nesterov [this message]
2011-01-18 2:11 ` Roland McGrath
2011-01-27 13:23 ` Tejun Heo
2011-01-28 21:06 ` Roland McGrath
2011-01-18 2:14 ` Roland McGrath
2011-01-27 15:46 ` Tejun Heo
2011-01-27 17:48 ` Tejun Heo
2011-01-28 20:40 ` Roland McGrath
2011-01-31 15:41 ` Tejun Heo
2011-01-31 15:54 ` Oleg Nesterov
2011-01-31 16:07 ` Tejun Heo
2011-02-01 10:35 ` Tejun Heo
2011-02-02 5:39 ` Roland McGrath
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