From: Joel Fernandes <joel@joelfernandes•org>
To: Peter Zijlstra <peterz@infradead•org>
Cc: linux-kernel@vger•kernel.org,
Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>,
Bjorn Helgaas <bhelgaas@google•com>,
Borislav Petkov <bp@alien8•de>,
c0d1n61at3@gmail•com, "David S. Miller" <davem@davemloft•net>,
edumazet@google•com,
Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>,
"H. Peter Anvin" <hpa@zytor•com>, Ingo Molnar <mingo@redhat•com>,
Josh Triplett <josh@joshtriplett•org>,
keescook@chromium•org, kernel-hardening@lists•openwall.com,
Lai Jiangshan <jiangshanlai@gmail•com>,
Len Brown <lenb@kernel•org>,
linux-acpi@vger•kernel.org, linux-pci@vger•kernel.org,
linux-pm@vger•kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios•com>,
neilb@suse•com, netdev@vger•kernel.org, oleg@redhat•com,
"Paul E. McKenney" <paulmck@linux•ibm.com>,
Pavel Machek <pavel@ucw•cz>,
"Rafael J. Wysocki" <rjw@rjwysocki•net>,
Rasmus Villemoes <rasmus.villemoes@prevas•dk>,
rcu@vger•kernel.org, Steven Rostedt <rostedt@goodmis•org>,
Tejun Heo <tj@kernel•org>, Thomas Gleixner <tglx@linutronix•de>,
will@kernel•org,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel•org>
Subject: Re: [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader checking
Date: Fri, 12 Jul 2019 11:10:51 -0400 [thread overview]
Message-ID: <20190712151051.GB235410@google.com> (raw)
In-Reply-To: <20190712111125.GT3402@hirez.programming.kicks-ass.net>
On Fri, Jul 12, 2019 at 01:11:25PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 11, 2019 at 07:43:56PM -0400, Joel Fernandes (Google) wrote:
> > +int rcu_read_lock_any_held(void)
> > +{
> > + int lockdep_opinion = 0;
> > +
> > + if (!debug_lockdep_rcu_enabled())
> > + return 1;
> > + if (!rcu_is_watching())
> > + return 0;
> > + if (!rcu_lockdep_current_cpu_online())
> > + return 0;
> > +
> > + /* Preemptible RCU flavor */
> > + if (lock_is_held(&rcu_lock_map))
>
> you forgot debug_locks here.
Actually, it turns out debug_locks checking is not even needed. If
debug_locks == 0, then debug_lockdep_rcu_enabled() returns 0 and we would not
get to this point.
> > + return 1;
> > +
> > + /* BH flavor */
> > + if (in_softirq() || irqs_disabled())
>
> I'm not sure I'd put irqs_disabled() under BH, also this entire
> condition is superfluous, see below.
>
> > + return 1;
> > +
> > + /* Sched flavor */
> > + if (debug_locks)
> > + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> > + return lockdep_opinion || !preemptible();
>
> that !preemptible() turns into:
>
> !(preempt_count()==0 && !irqs_disabled())
>
> which is:
>
> preempt_count() != 0 || irqs_disabled()
>
> and already includes irqs_disabled() and in_softirq().
>
> > +}
>
> So maybe something lke:
>
> if (debug_locks && (lock_is_held(&rcu_lock_map) ||
> lock_is_held(&rcu_sched_lock_map)))
> return true;
Agreed, I will do it this way (without the debug_locks) like:
---8<-----------------------
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index ba861d1716d3..339aebc330db 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -296,27 +296,15 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
int rcu_read_lock_any_held(void)
{
- int lockdep_opinion = 0;
-
if (!debug_lockdep_rcu_enabled())
return 1;
if (!rcu_is_watching())
return 0;
if (!rcu_lockdep_current_cpu_online())
return 0;
-
- /* Preemptible RCU flavor */
- if (lock_is_held(&rcu_lock_map))
- return 1;
-
- /* BH flavor */
- if (in_softirq() || irqs_disabled())
- return 1;
-
- /* Sched flavor */
- if (debug_locks)
- lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
- return lockdep_opinion || !preemptible();
+ if (lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map))
+ return 1;
+ return !preemptible();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
next prev parent reply other threads:[~2019-07-12 15:10 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 23:43 [PATCH v1 0/6] Harden list_for_each_entry_rcu() and family Joel Fernandes (Google)
2019-07-11 23:43 ` [PATCH v1 1/6] rcu: Add support for consolidated-RCU reader checking Joel Fernandes (Google)
2019-07-12 4:49 ` Joel Fernandes
2019-07-12 11:01 ` Peter Zijlstra
2019-07-12 14:49 ` Joel Fernandes
2019-07-12 11:11 ` Peter Zijlstra
2019-07-12 15:10 ` Joel Fernandes [this message]
2019-07-12 15:58 ` Peter Zijlstra
2019-07-12 16:45 ` Paul E. McKenney
2019-07-12 17:06 ` Joel Fernandes
2019-07-12 17:46 ` Paul E. McKenney
2019-07-12 19:40 ` Joel Fernandes
2019-07-12 23:27 ` Paul E. McKenney
2019-07-12 12:12 ` Oleg Nesterov
2019-07-12 13:56 ` Joel Fernandes
2019-07-11 23:43 ` [PATCH v1 2/6] ipv4: add lockdep condition to fix for_each_entry Joel Fernandes (Google)
2019-07-11 23:43 ` [PATCH v1 3/6] driver/core: Convert to use built-in RCU list checking Joel Fernandes (Google)
2019-07-12 5:19 ` Greg Kroah-Hartman
2019-07-11 23:43 ` [PATCH v1 4/6] workqueue: Convert for_each_wq to use built-in list check Joel Fernandes (Google)
2019-07-11 23:44 ` [PATCH v1 5/6] x86/pci: Pass lockdep condition to pcm_mmcfg_list iterator Joel Fernandes (Google)
2019-07-11 23:44 ` [PATCH v1 6/6] acpi: Use built-in RCU list checking for acpi_ioremaps list Joel Fernandes (Google)
2019-07-11 23:52 ` [PATCH v1 0/6] Harden list_for_each_entry_rcu() and family Joel Fernandes
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