Commit 288e984e authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Steven Rostedt
Browse files

tracing/kprobes: Avoid perf_trace_buf_*() if ->perf_events is empty 

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().

Link: http://lkml.kernel.org/r/20130620173806.GA13151@redhat.com



Acked-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 6e94a780

kernel/trace/trace_kprobe.c

+8 −4
Original line number Diff line number Diff line
@@ -1156,6 +1156,10 @@ 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));
@@ -1171,8 +1175,6 @@ 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);

}
@@ -1188,6 +1190,10 @@ 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));
@@ -1203,8 +1209,6 @@ 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);

}

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