Re: [PATCH 1/3] tracing/kprobes: Avoid perf_trace_buf_*() if ->perf_events is empty

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2013/06/17 2:21), Oleg Nesterov wrote:
> perf_trace_buf_prepare() + perf_trace_buf_submit() make no sense
> if this task/CPU has no active counters. Change kprobe_perf_func()
> and kretprobe_perf_func() to check call->perf_events beforehand
> and return if this list is empty.
> 
> For example, "perf record -e some_probe -p1". Only /sbin/init will
> report, all other threads which hit the same probe will do
> perf_trace_buf_prepare/perf_trace_buf_submit just to realize that
> nobody wants perf_swevent_event().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Looks good :) Thank you!

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

> ---
>  kernel/trace/trace_kprobe.c |   12 ++++++++----
>  1 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 9f46e98..c0af476 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1157,6 +1157,10 @@ kprobe_perf_func(struct trace_probe *tp, struct pt_regs *regs)
>  	int size, __size, dsize;
>  	int rctx;
>  
> +	head = this_cpu_ptr(call->perf_events);
> +	if (hlist_empty(head))
> +		return;
> +
>  	dsize = __get_data_size(tp, regs);
>  	__size = sizeof(*entry) + tp->size + dsize;
>  	size = ALIGN(__size + sizeof(u32), sizeof(u64));
> @@ -1172,8 +1176,6 @@ kprobe_perf_func(struct trace_probe *tp, struct pt_regs *regs)
>  	entry->ip = (unsigned long)tp->rp.kp.addr;
>  	memset(&entry[1], 0, dsize);
>  	store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);
> -
> -	head = this_cpu_ptr(call->perf_events);
>  	perf_trace_buf_submit(entry, size, rctx,
>  					entry->ip, 1, regs, head, NULL);
>  }
> @@ -1189,6 +1191,10 @@ kretprobe_perf_func(struct trace_probe *tp, struct kretprobe_instance *ri,
>  	int size, __size, dsize;
>  	int rctx;
>  
> +	head = this_cpu_ptr(call->perf_events);
> +	if (hlist_empty(head))
> +		return;
> +
>  	dsize = __get_data_size(tp, regs);
>  	__size = sizeof(*entry) + tp->size + dsize;
>  	size = ALIGN(__size + sizeof(u32), sizeof(u64));
> @@ -1204,8 +1210,6 @@ kretprobe_perf_func(struct trace_probe *tp, struct kretprobe_instance *ri,
>  	entry->func = (unsigned long)tp->rp.kp.addr;
>  	entry->ret_ip = (unsigned long)ri->ret_addr;
>  	store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);
> -
> -	head = this_cpu_ptr(call->perf_events);
>  	perf_trace_buf_submit(entry, size, rctx,
>  					entry->ret_ip, 1, regs, head, NULL);
>  }
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com