linux-kernel - Re: [PATCH] sched.h: Annotate sighand_struct with _

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Date:   Mon, 27 Jan 2020 22:44:53 +0530
From:   Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     madhuparnabhowmik10@...il.com, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, ebiederm@...ssion.com,
        christian.brauner@...ntu.com, paulmck@...nel.org,
        joel@...lfernandes.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        frextrite@...il.com, rcu@...r.kernel.org
Subject: Re: [PATCH] sched.h: Annotate sighand_struct with __rcu

On Mon, Jan 27, 2020 at 10:29:52AM +0100, Oleg Nesterov wrote:
> On 01/24, madhuparnabhowmik10@...il.com wrote:
> >
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -918,7 +918,7 @@ struct task_struct {
> >  
> >  	/* Signal handlers: */
> >  	struct signal_struct		*signal;
> > -	struct sighand_struct		*sighand;
> > +	struct sighand_struct __rcu		*sighand;
> >  	sigset_t			blocked;
> >  	sigset_t			real_blocked;
> >  	/* Restored if set_restore_sigmask() was used: */
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index bcd46f547db3..9ad8dea93dbb 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -1383,7 +1383,7 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
> >  		 * must see ->sighand == NULL.
> >  		 */
> >  		spin_lock_irqsave(&sighand->siglock, *flags);
> > -		if (likely(sighand == tsk->sighand))
> > +		if (likely(sighand == rcu_access_pointer(tsk->sighand)))
> >  			break;
> >  		spin_unlock_irqrestore(&sighand->siglock, *flags);
> >  	}
> 
> ACK,
> 
> perhaps you can also cleanup copy_sighand(). rcu_assign_pointer() makes no
> sense, we should either move it down or simply use RCU_INIT_POINTER().
> 
Sure, I will do it and send a patch soon.

Thank you,
Madhuparna

> Oleg.
>