From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753582AbbJFRSq (ORCPT ); Tue, 6 Oct 2015 13:18:46 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:42559 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752782AbbJFRSo (ORCPT ); Tue, 6 Oct 2015 13:18:44 -0400 Date: Tue, 6 Oct 2015 10:18:39 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock() Message-ID: <20151006171839.GD9600@cloud> References: <20151006161305.GA9799@linux.vnet.ibm.com> <1444148028-11551-1-git-send-email-paulmck@linux.vnet.ibm.com> <1444148028-11551-7-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1444148028-11551-7-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote: > Currently, __srcu_read_lock() cannot be invoked from restricted > environments because it contains calls to preempt_disable() and > preempt_enable(), both of which can invoke lockdep, which is a bad > idea in some restricted execution modes. This commit therefore moves > the preempt_disable() and preempt_enable() from __srcu_read_lock() > to srcu_read_lock(). It also inserts the preempt_disable() and > preempt_enable() around the call to __srcu_read_lock() in do_exit(). What restricted environments do you intend to invoke __srcu_read_lock from? This change seems fine, but I don't see any change in this patch series that needs this, hence my curiosity. > Signed-off-by: Paul E. McKenney > --- > include/linux/srcu.h | 5 ++++- > kernel/exit.c | 2 ++ > kernel/rcu/srcu.c | 2 -- > 3 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > index bdeb4567b71e..f5f80c5643ac 100644 > --- a/include/linux/srcu.h > +++ b/include/linux/srcu.h > @@ -215,8 +215,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp) > */ > static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) > { > - int retval = __srcu_read_lock(sp); > + int retval; > > + preempt_disable(); > + retval = __srcu_read_lock(sp); > + preempt_enable(); > rcu_lock_acquire(&(sp)->dep_map); > return retval; > } > diff --git a/kernel/exit.c b/kernel/exit.c > index ea95ee1b5ef7..0e93b63bbc59 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -761,7 +761,9 @@ void do_exit(long code) > */ > flush_ptrace_hw_breakpoint(tsk); > > + TASKS_RCU(preempt_disable()); > TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu)); > + TASKS_RCU(preempt_enable()); > exit_notify(tsk, group_dead); > proc_exit_connector(tsk); > #ifdef CONFIG_NUMA > diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c > index 9e6122540d28..a63a1ea5a41b 100644 > --- a/kernel/rcu/srcu.c > +++ b/kernel/rcu/srcu.c > @@ -298,11 +298,9 @@ int __srcu_read_lock(struct srcu_struct *sp) > int idx; > > idx = READ_ONCE(sp->completed) & 0x1; > - preempt_disable(); > __this_cpu_inc(sp->per_cpu_ref->c[idx]); > smp_mb(); /* B */ /* Avoid leaking the critical section. */ > __this_cpu_inc(sp->per_cpu_ref->seq[idx]); > - preempt_enable(); > return idx; > } > EXPORT_SYMBOL_GPL(__srcu_read_lock); > -- > 2.5.2 >