From b2fe8ba674e8acbb9e8e63510b802c6d054d88a3 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Mon, 4 Feb 2013 19:05:43 +0100
Subject: [PATCH] uprobes/perf: Avoid uprobe_apply() whenever possible

uprobe_perf_open/close call the costly uprobe_apply() every time,
we can avoid it if:

	- "nr_systemwide != 0" is not changed.

	- There is another process/thread with the same ->mm.

	- copy_proccess() does inherit_event(). dup_mmap() preserves the
	  inserted breakpoints.

	- event->attr.enable_on_exec == T, we can rely on uprobe_mmap()
	  called by exec/mmap paths.

	- tp_target is exiting. Only _close() checks PF_EXITING, I don't
	  think TRACE_REG_PERF_OPEN can hit the dying task too often.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
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