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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>
This commit is contained in:
Oleg Nesterov 2013-04-13 15:36:49 +02:00
parent 32520b2c69
commit 515619f209
1 changed files with 4 additions and 1 deletions
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5
kernel/trace/trace_uprobe.c
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@ -820,6 +820,10 @@ static void uprobe_perf_print(struct trace_uprobe *tu,
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 @@ static void uprobe_perf_print(struct trace_uprobe *tu,
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();