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

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Message-ID: <20140410133435.GB12228@redhat.com>
Date:	Thu, 10 Apr 2014 15:34:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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 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.

> > @@ -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.

Oleg.

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