linux-kernel - Re: [PATCH v8 4/7] cgroup: cgroup v2 freezer

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Date:   Wed, 20 Feb 2019 22:14:29 +0000
From:   Roman Gushchin <guro@...com>
To:     Oleg Nesterov <oleg@...hat.com>
CC:     Roman Gushchin <guroan@...il.com>, Tejun Heo <tj@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 4/7] cgroup: cgroup v2 freezer

On Wed, Feb 20, 2019 at 03:42:02PM +0100, Oleg Nesterov wrote:
> On 02/19, Roman Gushchin wrote:
> >
> > @@ -2065,6 +2066,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t
> >  		preempt_disable();
> >  		read_unlock(&tasklist_lock);
> >  		preempt_enable_no_resched();
> > +		cgroup_enter_stopped();
> >  		freezable_schedule();
> >  	} else {
> >  		/*
> > @@ -2243,6 +2245,7 @@ static bool do_signal_stop(int signr)
> >  		}
> >  
> >  		/* Now we don't run again until woken by SIGCONT or SIGKILL */
> > +		cgroup_enter_stopped();
> >  		freezable_schedule();
> >  		return true;
> 
> Please see my reply to 0/7.

Answered in that thread.

> 
> > @@ -2280,7 +2286,8 @@ static void do_jobctl_trap(void)
> >  		    !(signal->flags & SIGNAL_STOP_STOPPED))
> >  			signr = SIGTRAP;
> >  		WARN_ON_ONCE(!signr);
> > -		ptrace_do_notify(signr, signr | (PTRACE_EVENT_STOP << 8),
> > +		ptrace_do_notify(signr,
> > +				 signr | (PTRACE_EVENT_STOP << 8),
> >  				 CLD_STOPPED);
> 
> white-space cleanup?

Sorry, a bogus change. Please, ignore it.

> 
> > @@ -2363,7 +2419,8 @@ bool get_signal(struct ksignal *ksig)
> >  	 * we should notify the parent, prepare_signal(SIGCONT) encodes
> >  	 * the CLD_ si_code into SIGNAL_CLD_MASK bits.
> >  	 */
> > -	if (unlikely(signal->flags & SIGNAL_CLD_MASK)) {
> > +	if (unlikely(signal->flags & SIGNAL_CLD_MASK) &
> > +	    !(current->jobctl & JOBCTL_TRAP_FREEZE)) {
> 
> Hmm, why?

If a process is going from the stopped to the frozen state, it looks like
it's better to delay parent's notification up to the moment when it will
actually run.

Thanks!