From: Steven Rostedt <srostedt@redhat.com>
Date: Wed, 3 Dec 2008 16:04:51 +0000 (-0500)
Subject: ftrace: fix race in function graph during fork
X-Git-Tag: v2.6.29-rc1~586^2~34^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e8e1abe92fd7ea9d823a3aaf81d10e2cba593b6b;p=pandora-kernel.git

ftrace: fix race in function graph during fork

Impact: graph tracer race/crash fix

There is a nasy race in startup of a new process running the
function graph tracer. In fork.c:

	total_forks++;
	spin_unlock(&current->sighand->siglock);
	write_unlock_irq(&tasklist_lock);
	ftrace_graph_init_task(p);
	proc_fork_connector(p);
	cgroup_post_fork(p);
	return p;

The new task is free to run as soon as the tasklist_lock is released.
This is before the ftrace_graph_init_task. If the task does run
it will be using the same ret_stack and curr_ret_stack as the parent.
This will cause crashes that are difficult to debug.

This patch moves the ftrace_graph_init_task to just after the alloc_pid
code. This fixes the above race.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

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