From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu,
KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
Michel Lespinasse <walken@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH tip/core/rcu 01/11] mm: Place preemption point in do_mlockall() loop
Date: Wed, 25 Sep 2013 13:18:20 -0700 [thread overview]
Message-ID: <20130925201820.GA9093@linux.vnet.ibm.com> (raw)
In-Reply-To: <20130925123537.c948095dd10fbf6e1b8708f4@linux-foundation.org>
On Wed, Sep 25, 2013 at 12:35:37PM -0700, Andrew Morton wrote:
> On Wed, 25 Sep 2013 06:48:04 -0700 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > On Tue, Sep 24, 2013 at 09:10:47PM -0700, Andrew Morton wrote:
> > > On Tue, 24 Sep 2013 18:29:11 -0700 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> > >
> > > > --- a/mm/mlock.c
> > > > +++ b/mm/mlock.c
> > > > @@ -736,6 +736,7 @@ static int do_mlockall(int flags)
> > > >
> > > > /* Ignore errors */
> > > > mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
> > > > + cond_resched();
> > > > }
> > > > out:
> > > > return 0;
> > >
> > > Might need one in munlock_vma_pages_range() as well - it's a matter of
> > > finding the right test case. This will be neverending :(
> >
> > Indeed... I suspect that Trinity running on big-memory systems will
> > eventually find most of them via RCU CPU stall warnings, but as you say...
> >
> > Would you like the corresponding change to munlock_vma_pages_range()
> > beforehand?
>
> Can't decide. If we went and poked holes in every place which looks
> like it loops for a long time, we'd be poking holes everywhere, some of
> them unnecessary. otoh if we wait around for people to say "hey" then
> it will take a very long time to poke all the needed holes.
Yep.
> The best approach would be for someone to sit down, identify all the
> potential problem spots, attempt to craft a userspace exploit to verify
> that each one really is a problem, then fix it. Nobody will bother
> doing this.
And if someone does bother doing this, there will no doubt be some debate
about whether or not the exploit is reasonable.
> So I dunno. Stop asking difficult questions ;)
;-) ;-) ;-)
Thanx, Paul
prev parent reply other threads:[~2013-09-25 20:18 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-25 1:27 [PATCH tip/core/rcu 0/11] Fixes for 3.13 Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 01/11] mm: Place preemption point in do_mlockall() loop Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 02/11] rcu: Use proper cpp macro for ->gp_flags Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 03/11] rcu: Convert local functions to static Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 04/11] rcu: Fix dubious "if" condition in __call_rcu_nocb_enqueue() Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 05/11] rcu: Make list_splice_init_rcu() account for RCU readers Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 06/11] rcu: Replace __get_cpu_var() uses Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 07/11] rcu: Silence unused-variable warnings Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 08/11] rcu: Micro-optimize rcu_cpu_has_callbacks() Paul E. McKenney
2013-09-25 2:55 ` Chen Gang
2013-09-25 20:16 ` Paul E. McKenney
2013-09-26 2:57 ` Chen Gang
2013-09-26 18:33 ` Paul E. McKenney
2013-09-27 2:29 ` Chen Gang
2013-09-29 4:24 ` Chen Gang
2013-09-29 20:23 ` Paul E. McKenney
2013-09-30 1:33 ` Chen Gang
2013-09-25 1:29 ` [PATCH tip/core/rcu 09/11] rcu: Reject memory-order-induced stall-warning false positives Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 10/11] rcu: Have rcutiny tracepoints use tracepoint_string() Paul E. McKenney
2013-09-25 1:29 ` [PATCH tip/core/rcu 11/11] rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask Paul E. McKenney
2013-09-25 4:10 ` [PATCH tip/core/rcu 01/11] mm: Place preemption point in do_mlockall() loop Andrew Morton
2013-09-25 13:48 ` Paul E. McKenney
2013-09-25 19:35 ` Andrew Morton
2013-09-25 20:18 ` Paul E. McKenney [this message]
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