linux-kernel - Re: [PATCH tip/core/rcu 20/41] kprobes: eplace synchronize_sched() with synchronize

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Date:   Sun, 11 Nov 2018 19:19:16 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH tip/core/rcu 20/41] kprobes: eplace synchronize_sched()
 with synchronize_rcu()

On Mon, Nov 12, 2018 at 12:00:48PM +0900, Masami Hiramatsu wrote:
> On Sun, 11 Nov 2018 11:43:49 -0800
> "Paul E. McKenney" <paulmck@...ux.ibm.com> wrote:
> 
> > Now that synchronize_rcu() waits for preempt-disable regions of code
> > as well as RCU read-side critical sections, synchronize_sched() can be
> > replaced by synchronize_rcu().  This commit therefore makes this change.
> 
> Would you mean synchronize_rcu() can ensure that any interrupt handler
> (which should run under preempt-disable state) run out (even on non-preemptive
> kernel)?

Yes, but only as of this merge window.  See this commit:

3e3100989869 ("rcu: Defer reporting RCU-preempt quiescent states when disabled")

Don't try this in v4.19 or earlier, but v4.20 and later is OK.  ;-)

							Thanx, Paul

> If so, I agree with these changes.
> 
> Thank you,
> 
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
> > Cc: "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
> > Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  kernel/kprobes.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 90e98e233647..08e31d863191 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -229,7 +229,7 @@ static int collect_garbage_slots(struct kprobe_insn_cache *c)
> >  	struct kprobe_insn_page *kip, *next;
> >  
> >  	/* Ensure no-one is interrupted on the garbages */
> > -	synchronize_sched();
> > +	synchronize_rcu();
> >  
> >  	list_for_each_entry_safe(kip, next, &c->pages, list) {
> >  		int i;
> > @@ -1382,7 +1382,7 @@ static int register_aggr_kprobe(struct kprobe *orig_p, struct kprobe *p)
> >  			if (ret) {
> >  				ap->flags |= KPROBE_FLAG_DISABLED;
> >  				list_del_rcu(&p->list);
> > -				synchronize_sched();
> > +				synchronize_rcu();
> >  			}
> >  		}
> >  	}
> > @@ -1597,7 +1597,7 @@ int register_kprobe(struct kprobe *p)
> >  		ret = arm_kprobe(p);
> >  		if (ret) {
> >  			hlist_del_rcu(&p->hlist);
> > -			synchronize_sched();
> > +			synchronize_rcu();
> >  			goto out;
> >  		}
> >  	}
> > @@ -1776,7 +1776,7 @@ void unregister_kprobes(struct kprobe **kps, int num)
> >  			kps[i]->addr = NULL;
> >  	mutex_unlock(&kprobe_mutex);
> >  
> > -	synchronize_sched();
> > +	synchronize_rcu();
> >  	for (i = 0; i < num; i++)
> >  		if (kps[i]->addr)
> >  			__unregister_kprobe_bottom(kps[i]);
> > @@ -1966,7 +1966,7 @@ void unregister_kretprobes(struct kretprobe **rps, int num)
> >  			rps[i]->kp.addr = NULL;
> >  	mutex_unlock(&kprobe_mutex);
> >  
> > -	synchronize_sched();
> > +	synchronize_rcu();
> >  	for (i = 0; i < num; i++) {
> >  		if (rps[i]->kp.addr) {
> >  			__unregister_kprobe_bottom(&rps[i]->kp);
> > -- 
> > 2.17.1
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@...nel.org>
>