From: Tejun Heo <tj@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: jan.kratochvil@redhat.com, vda.linux@googlemail.com,
linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
akpm@linux-foundation.org, indan@nul.nu, roland@hack.frob.com
Subject: Re: [PATCHSET] ptrace,signal: Improve ptrace and job control interaction
Date: Fri, 25 Mar 2011 15:26:30 +0100 [thread overview]
Message-ID: <20110325142630.GD1409@htj.dyndns.org> (raw)
In-Reply-To: <20110323183837.GA27680@redhat.com>
Hello, Oleg.
On Wed, Mar 23, 2011 at 07:38:37PM +0100, Oleg Nesterov wrote:
> But of course we need more changes. In particular, there is still the
> small problem with the CLD_CONTINUED notification.
>
> __ptrace_unlink() does signal_wake_up() if it adds SIGNAL_STOP_STOPPED.
> This is correct, but it should also add TIF_SIGPENDING if
> (signal->flags & SIGNAL_CLD_MASK) != 0.
>
> Otherwise, if the stopped tracee was PTRACE_CONT'ed and then SIGCONT
> ends the group-stop, the real_parent won't be notified after detach.
Heh, that's an interesting one. I don't think it has much to do with
__ptrace_unlink() tho. Isn't the proper solution using something akin
to signal_wake_up() in SIGCONT generation path in prepare_signal()?
Explicit wake_up_state() without kick_process() is okay there because
if the code assumes that the tasks are guaranteed to pass through
signal delivery path whenever event worthy of notification happens
(either SIGNAL_STOP_STOPPED or group_stop_count is set). PTRACE_CONT
breaks that as the tracee could be running in userland and thus the
solution is to add kick_process() as in signal_wake_up().
Am I making any sense?
> Unfortunately, this means that recalc_sigpending_tsk() has to check
> SIGNAL_CLD_MASK as well. Do you see another solution?
Hmmm... I think the above subtle breakage exists for !ptrace case too.
Please consider the following scenario.
* SIGSTOP is sent to a task and group stop is initiated.
* Before the task participates in group stop, SIGCONT is sent.
* Before CLD_STOPPED notification for the incomplete-stop/cont
sequence can be made, recalc_sigpending() happens.
* CLD_STOPPED notification is pending but TIF_SIGPENDING isn't set and
the task isn't in signal delivery path and can continue execution.
It's a pretty convoluted extremely unlikely corner case tho. Anyways,
adding SIGNAL_CLD_MASK test to recalc_sigpending() should solve it.
> There is another case. SIGCONT can hit the stopped-but-running-task,
> but I don't think we should try to set TIF_SIGPENDING in this case,
> you are going to add the trap later.
Hmmm... As I wrote above, I think we should do it regardless of the
new trap.
Thanks.
--
tejun
next prev parent reply other threads:[~2011-03-25 14:26 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-23 10:05 [PATCHSET] ptrace,signal: Improve ptrace and job control interaction Tejun Heo
2011-03-23 10:05 ` [PATCH 01/20] signal: Fix SIGCONT notification code Tejun Heo
2011-03-23 10:05 ` [PATCH 02/20] ptrace: Remove the extra wake_up_state() from ptrace_detach() Tejun Heo
2011-03-23 10:05 ` [PATCH 03/20] signal: Remove superflous try_to_freeze() loop in do_signal_stop() Tejun Heo
2011-03-23 10:05 ` [PATCH 04/20] ptrace: Kill tracehook_notify_jctl() Tejun Heo
2011-03-23 10:05 ` [PATCH 05/20] ptrace: Add @why to ptrace_stop() Tejun Heo
2011-03-23 10:05 ` [PATCH 06/20] signal: Fix premature completion of group stop when interfered by ptrace Tejun Heo
2011-03-23 10:05 ` [PATCH 07/20] signal: Use GROUP_STOP_PENDING to stop once for a single group stop Tejun Heo
2011-03-23 10:05 ` [PATCH 08/20] ptrace: Participate in group stop from ptrace_stop() iff the task is trapping for " Tejun Heo
2011-03-23 10:05 ` [PATCH 09/20] ptrace: Make do_signal_stop() use ptrace_stop() if the task is being ptraced Tejun Heo
2011-03-23 10:05 ` [PATCH 10/20] ptrace: Clean transitions between TASK_STOPPED and TRACED Tejun Heo
2011-03-23 10:05 ` [PATCH 11/20] ptrace: Collapse ptrace_untrace() into __ptrace_unlink() Tejun Heo
2011-03-23 10:05 ` [PATCH 12/20] ptrace: Always put ptracee into appropriate execution state Tejun Heo
2011-03-23 10:05 ` [PATCH 13/20] job control: Don't set group_stop exit_code if re-entering job control stop Tejun Heo
2011-03-23 10:06 ` [PATCH 14/20] job control: Small reorganization of wait_consider_task() Tejun Heo
2011-03-23 10:06 ` [PATCH 15/20] job control: Fix ptracer wait(2) hang and explain notask_error clearing Tejun Heo
2011-03-23 10:06 ` [PATCH 16/20] job control: Allow access to job control events through ptracees Tejun Heo
2011-03-23 10:06 ` [PATCH 17/20] job control: Add @for_ptrace to do_notify_parent_cldstop() Tejun Heo
2011-03-23 10:06 ` [PATCH 18/20] job control: Job control stop notifications should always go to the real parent Tejun Heo
2011-03-23 10:06 ` [PATCH 19/20] job control: Notify the real parent of job control events regardless of ptrace Tejun Heo
2011-03-23 10:06 ` [PATCH 20/20] job control: Don't send duplicate job control stop notification while ptraced Tejun Heo
2011-03-23 18:38 ` [PATCHSET] ptrace,signal: Improve ptrace and job control interaction Oleg Nesterov
2011-03-25 14:26 ` Tejun Heo [this message]
2011-03-26 18:25 ` Oleg Nesterov
2011-03-28 8:58 ` Tejun Heo
2011-03-28 12:14 ` Oleg Nesterov
2011-03-28 15:21 ` Tejun Heo
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