lkml.org 
[lkml]   [2012]   [Aug]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: lockdep warning on rt_mutex_lock()
On Sat, Aug 18, 2012 at 12:59:08PM +0800, Fengguang Wu wrote:
> On Fri, Aug 17, 2012 at 07:44:37AM -0700, Paul E. McKenney wrote:
> > On Fri, Aug 17, 2012 at 10:02:40PM +0800, Fengguang Wu wrote:
> > > On Fri, Aug 17, 2012 at 06:43:28AM -0700, Paul E. McKenney wrote:
> > > > On Fri, Aug 17, 2012 at 06:06:35PM +0800, Fengguang Wu wrote:
> > > > > Greetings,
> > > > >
> > > > > FYI, a lockdep warning:
> > > >
> > > > Certainly looks problematic!
> > > >
> > > > Any hint as to what version of the kernel produced this splat?
> > > > (Yes, lazy of me to ask, I know, but I am not seeing it in my testing.)
> > >
> > > It happens on both 3.5.0 and 3.6-rc1. Will bisect (try older kernels) help?
> > > Bisect is handy for me :)
> >
> > Bisection would be very welcome!!! ;-)
>
> The bisect result is...

Hmmm... This patch is a bit of a blast from the past.

> commit 9e571a82f0cb205a65a0ea41657f19f22b7fabb8
> Author: Paul E. McKenney <paul.mckenney@linaro.org>
> Date: Thu Sep 30 21:26:52 2010 -0700
>
> rcu: add tracing for TINY_RCU and TINY_PREEMPT_RCU
>
> Add tracing for the tiny RCU implementations, including statistics on
> boosting in the case of TINY_PREEMPT_RCU and RCU_BOOST.
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

So the lockdep complaint indicates that lockdep and the actual hardware
had different opinions about whether or not interrupts were enabled.
One way that can happen is through use of raw_local_irq_save(). And this
commit did add a raw_local_irq_save().

So maybe converting to local_irq_save() will make things work better.

Fengguang, could you please try out the following patch?

Thanx, Paul

------------------------------------------------------------------------

rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save()

The use of raw_local_irq_save() is unnecessary, given that local_irq_save()
really does disable interrupts. Also, it appears to interfere with lockdep.
Therefore, this commit moves to local_irq_save().

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 918fd1e..3d01902 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -278,7 +278,7 @@ static int rcu_boost(void)
rcu_preempt_ctrlblk.exp_tasks == NULL)
return 0; /* Nothing to boost. */

- raw_local_irq_save(flags);
+ local_irq_save(flags);

/*
* Recheck with irqs disabled: all tasks in need of boosting
@@ -287,7 +287,7 @@ static int rcu_boost(void)
*/
if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
rcu_preempt_ctrlblk.exp_tasks == NULL) {
- raw_local_irq_restore(flags);
+ local_irq_restore(flags);
return 0;
}

@@ -317,7 +317,7 @@ static int rcu_boost(void)
t = container_of(tb, struct task_struct, rcu_node_entry);
rt_mutex_init_proxy_locked(&mtx, t);
t->rcu_boost_mutex = &mtx;
- raw_local_irq_restore(flags);
+ local_irq_restore(flags);
rt_mutex_lock(&mtx);
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */

@@ -991,9 +991,9 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
{
unsigned long flags;

- raw_local_irq_save(flags);
+ local_irq_save(flags);
rcp->qlen -= n;
- raw_local_irq_restore(flags);
+ local_irq_restore(flags);
}

/*


\
 
 \ /
  Last update: 2012-08-21 22:01    [W:0.089 / U:6.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site