linux-kernel - Re: [PATCH RESEND 1/2] tracing: syscall_*regfunc() can race with copy

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Message-ID: <20140411112259.79f0a0ba@gandalf.local.home>
Date:	Fri, 11 Apr 2014 11:22:59 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH RESEND 1/2] tracing: syscall_*regfunc() can race with
 copy_process()

On Thu, 10 Apr 2014 15:34:35 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> On 04/10, Steven Rostedt wrote:
> >
> > On Wed, 9 Apr 2014 19:05:42 +0200
> > Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > > --- a/kernel/fork.c
> > > +++ b/kernel/fork.c
> > > @@ -1472,7 +1472,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> > >
> > >  	total_forks++;
> > >  	spin_unlock(&current->sighand->siglock);
> > > +	syscall_tracepoint_update(p);
> > >  	write_unlock_irq(&tasklist_lock);
> > > +
> >
> > So this looks to be a fix that probably should go to stable?
> 
> Not sure, this is up to you.

I'll have to think about this one, whether or not it should go to
stable.

> 
> > > @@ -732,33 +732,31 @@ static int sys_tracepoint_refcount;
> > >
> > >  void syscall_regfunc(void)
> > >  {
> > > -	unsigned long flags;
> > >  	struct task_struct *g, *t;
> > >
> > >  	if (!sys_tracepoint_refcount) {
> > > -		read_lock_irqsave(&tasklist_lock, flags);
> > > +		read_lock(&tasklist_lock);
> > >  		do_each_thread(g, t) {
> > >  			/* Skip kernel threads. */
> > > -			if (t->mm)
> > > +			if (!(t->flags & PF_KTHREAD))
> > >  				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> > >  		} while_each_thread(g, t);
> > > -		read_unlock_irqrestore(&tasklist_lock, flags);
> > > +		read_unlock(&tasklist_lock);
> > >  	}
> > >  	sys_tracepoint_refcount++;
> > >  }
> > >
> > >  void syscall_unregfunc(void)
> > >  {
> > > -	unsigned long flags;
> > >  	struct task_struct *g, *t;
> > >
> > >  	sys_tracepoint_refcount--;
> > >  	if (!sys_tracepoint_refcount) {
> > > -		read_lock_irqsave(&tasklist_lock, flags);
> > > +		read_lock(&tasklist_lock);
> > >  		do_each_thread(g, t) {
> > >  			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
> > >  		} while_each_thread(g, t);
> > > -		read_unlock_irqrestore(&tasklist_lock, flags);
> > > +		read_unlock(&tasklist_lock);
> >
> > These changes should be in a separate patch, as they can wait till 3.16.
> 
> OK, I'll split this change.

Are you going to send a new series?

-- Steve

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