uprobes/perf: Avoid perf_trace_buf_prepare/submit 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 uprobe_perf_print()
to return if hlist_empty(call->perf_events).
Note: this is not uprobe-specific, we can change other users too.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 37ccb72..32494fb0 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -820,6 +820,10 @@
return;
preempt_disable();
+ head = this_cpu_ptr(call->perf_events);
+ if (hlist_empty(head))
+ goto out;
+
entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
if (!entry)
goto out;
@@ -836,7 +840,6 @@
for (i = 0; i < tu->nr_args; i++)
call_fetch(&tu->args[i].fetch, regs, data + tu->args[i].offset);
- head = this_cpu_ptr(call->perf_events);
perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
out:
preempt_enable();
