linux-kernel - Re: Testing tracer wakeup_rt: .. no entries found ..FAILED!

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Message-ID: <20120801001811.GX2422@linux.vnet.ibm.com>
Date:	Tue, 31 Jul 2012 17:18:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Fengguang Wu <fengguang.wu@...el.com>, Avi Kivity <avi@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: Testing tracer wakeup_rt: .. no entries found ..FAILED!

On Tue, Jul 31, 2012 at 08:09:38PM -0400, Steven Rostedt wrote:
> On Tue, 2012-07-31 at 16:57 -0700, Paul E. McKenney wrote:
> 
> > > What was the next lines? I bet you it was "PASSED". Which means it did
> > > not fail. This is the second bug you found that has to do with RCU being
> > > called in 'idle'. The one that Paul posted a patch for.
> > 
> > Though it needs another patch to actually use it in the right place...
> 
> Right. Something like this:

Looks good to me!

							Thanx, Paul

> -- Steve
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 5638104..d915638 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -631,7 +631,12 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
> 
>  	memcpy(max_data->comm, tsk->comm, TASK_COMM_LEN);
>  	max_data->pid = tsk->pid;
> -	max_data->uid = task_uid(tsk);
> +	/*
> +	 * task_uid() calls rcu_read_lock, but this can be called
> +	 * outside of RCU state monitoring (irq going back to idle).
> +	 */ 
> +	RCU_NONIDLE(max_data->uid = task_uid(tsk));
> +
>  	max_data->nice = tsk->static_prio - 20 - MAX_RT_PRIO;
>  	max_data->policy = tsk->policy;
>  	max_data->rt_priority = tsk->rt_priority;
> 
> 

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