linux-kernel - Re: [PATCH] ringbuffer: synchronize for resizing

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Message-Id: <1257262540.26028.3336.camel@gandalf.stny.rr.com>
Date:	Tue, 03 Nov 2009 10:35:40 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ringbuffer: synchronize for resizing


On Tue, 2009-11-03 at 19:42 +0800, Lai Jiangshan wrote:
> We got a sudden panic when we reduced the size of the
> ringbuffer.
> 
> We can reproduce the panic by the following steps:
> 
> echo 1 > events/sched/enable
> cat trace_pipe > /dev/null &
> 
> while ((1))
> do
> echo 12000 > buffer_size_kb
> echo 512 > buffer_size_kb
> done
> 
> (not more than 5 seconds, panic ...)

Thanks! I'll push this out for inclusion right away.

-- Steve

> 
> Reported-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 63446f1..db223fe 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1196,6 +1196,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
>  	atomic_inc(&cpu_buffer->record_disabled);
>  	synchronize_sched();
>  
> +	spin_lock_irq(&cpu_buffer->reader_lock);
>  	rb_head_page_deactivate(cpu_buffer);
>  
>  	for (i = 0; i < nr_pages; i++) {
> @@ -1210,6 +1211,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
>  		return;
>  
>  	rb_reset_cpu(cpu_buffer);
> +	spin_unlock_irq(&cpu_buffer->reader_lock);
>  
>  	rb_check_pages(cpu_buffer);
>  
> 
> 
> 

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