linux-kernel - Re: [RT] sysrq Z: sleeping function called from invalid context

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Date:	Fri, 2 Dec 2011 16:27:22 -0800
From:	Frank Rowand <frank.rowand@...sony.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	"Rowand, Frank" <Frank_Rowand@...yusa.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>
Subject: Re: [RT] sysrq Z: sleeping function called from invalid context

On 12/02/11 15:49, Steven Rostedt wrote:
> On Fri, 2011-12-02 at 15:08 -0800, Frank Rowand wrote:
>> Hi Steve,
>>
>> I get a "sleeping function called from invalid context" when I invoke sysrq Z.
>>
>> I get this both with CONFIG_MAGIC_SYSRQ_FORCE_PRINTK enabled and disabled.
> 
> Patient:  Hey doctor, it hurts when I do this
> 
> Doctor:  Don't do that.

I had similar thoughts as I was writing my email.

< snip >

> 
> Oh! looking into the ring_buffer code, could you add this:
> (totally untested)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 2467714..2ffbb9d 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1045,7 +1045,7 @@ static inline int ok_to_lock(void)
>  	if (in_nmi())
>  		return 0;
>  #ifdef CONFIG_PREEMPT_RT_FULL
> -	if (in_atomic())
> +	if (in_atomic() || irqs_disabled())
>  		return 0;
>  #endif
>  	return 1;

I would say the result is good with the patch applied.

If CONFIG_MAGIC_SYSRQ_FORCE_PRINTK is disabled then the splat does not occur
and the ftrace buffer is printed on the console.

If CONFIG_MAGIC_SYSRQ_FORCE_PRINTK is enabled, then the splat does not occur
and the ftrace buffer sometimes is printed on the console.  I think that
this is good enough, given that sysrq when CONFIG_PREEMPT_RT_FULL is enabled
is somewhat dicey to begin with.

-Frank

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