linux-kernel - Re: [PATCH 3/4] uprobes/tracing: Kill the pointless local_save_flags/preempt

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Date:	Tue, 2 Apr 2013 10:58:27 +0200
From:	Anton Arapov <anton@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] uprobes/tracing: Kill the pointless
 local_save_flags/preempt_count calls

On Fri, Mar 29, 2013 at 07:15:45PM +0100, Oleg Nesterov wrote:
> uprobe_trace_func() is never called with irqs or preemption
> disabled, no need to ask preempt_count() or local_save_flags().
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/trace/trace_uprobe.c |   10 +++-------
>  1 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 8e00901..43d258d 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -492,17 +492,13 @@ static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  	struct ring_buffer_event *event;
>  	struct ring_buffer *buffer;
>  	u8 *data;
> -	int size, i, pc;
> -	unsigned long irq_flags;
> +	int size, i;
>  	struct ftrace_event_call *call = &tu->call;
>  
> -	local_save_flags(irq_flags);
> -	pc = preempt_count();
> -
>  	size = sizeof(*entry) + tu->size;
>  
>  	event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
> -						  size, irq_flags, pc);
> +						  size, 0, 0);
>  	if (!event)
>  		return 0;
>  
> @@ -513,7 +509,7 @@ static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  		call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
>  
>  	if (!filter_current_check_discard(buffer, call, entry, event))
> -		trace_buffer_unlock_commit(buffer, event, irq_flags, pc);
> +		trace_buffer_unlock_commit(buffer, event, 0, 0);
>  
>  	return 0;
>  }
> -- 
> 1.5.5.1
> 
Acked-by: Anton Arapov <anton@...hat.com>
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