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From: Oleg Nesterov <oleg@redhat.com>
To: Tejun Heo <tj@kernel.org>
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: Mon, 28 Mar 2011 14:14:01 +0200	[thread overview]
Message-ID: <20110328121401.GA4099@redhat.com> (raw)
In-Reply-To: <20110328085824.GE16530@htj.dyndns.org>

On 03/28, Tejun Heo wrote:
>
> Hey,
>
> On Sat, Mar 26, 2011 at 07:25:54PM +0100, Oleg Nesterov wrote:
> > > 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?
> >
> > Perhaps. This depends on how we define/implement the new behaviour.
> >
> > It is not clear to me what the new trap should actually do. And how.
> > Either way, prepare_signal(SIGCONT) should do something with the
> > ptraced threads, and this is what we should care about. Probably
> > we can set TIF_SIGPENDING if task_ptrace() is true.
> >
> > Anyway we should ensure SIGCONT can't race with detach.
>
> Hmmm... setting TIF_SIGPENDING and kicking the task to enter signal
> delivery path doesn't have any side effect when it's running in
> userland,

Yes. We should avoid the spurious TIF_SIGPENDING, if possible. But in
this case we don't care.

But, unless the thread is ptraced, it can't be running in userland,
why should we set TIF_SIGPENDING?

> > > * 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.
> >
> > This doesn't matter, or I misunderstood.
> >
> > We only add "SIGNAL_CLD_* | SIGNAL_STOP_CONTINUED" if we know there
> > is at least one thread in get_signal_to_deliver()->do_signal_stop()
> > paths. In this case we do not rely on TIF_SIGPENDING at all.
>
> We set SIGNAL_CLD_STOPPED if group_stop_count wasn't zero, ie. if
> group stop has initiated, which will be delivered as soon as any task
> enters signal delivery path.

Yes. And that task T has already called do_signal_stop() and it is
TASK_STOPPED.

> So, there's a path that we schedule a
> notification and doesn't enforce the delivery until something happens

prepare_signal(SIGCONT) wakes up all threads, including T. Once it
returns from do_signal_stop() to get_signal_to_deliver(), it will
check signal->flags.

> and a task in the group gets called into signal delivery path somehow,
> which is wrong.

Afaics, no. No need to force any thread to enter into the signal
delivery path. If group_stop_count != 0 (or SIGNAL_STOP_STOPPED is
set) there must be at least one thread which should _return_ to
get_signal_to_deliver() after wakeup.

No?

Oleg.


  reply	other threads:[~2011-03-28 13:23 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
2011-03-26 18:25     ` Oleg Nesterov
2011-03-28  8:58       ` Tejun Heo
2011-03-28 12:14         ` Oleg Nesterov [this message]
2011-03-28 15:21           ` Tejun Heo

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