• Steven Rostedt's avatar
    ftrace: Fix memory leak with function graph and cpu hotplug · 868baf07
    Steven Rostedt authored
    When the fuction graph tracer starts, it needs to make a special
    stack for each task to save the real return values of the tasks.
    All running tasks have this stack created, as well as any new
    On CPU hot plug, the new idle task will allocate a stack as well
    when init_idle() is called. The problem is that cpu hotplug does
    not create a new idle_task. Instead it uses the idle task that
    existed when the cpu went down.
    ftrace_graph_init_task() will add a new ret_stack to the task
    that is given to it. Because a clone will make the task
    have a stack of its parent it does not check if the task's
    ret_stack is already NULL or not. When the CPU hotplug code
    starts a CPU up again, it will allocate a new stack even
    though one already existed for it.
    The solution is to treat the idle_task specially. In fact, the
    function_graph code already does, just not at init_idle().
    Instead of using the ftrace_graph_init_task() for the idle task,
    which that function expects the task to be a clone, have a
    separate ftrace_graph_init_idle_task(). Also, we will create a
    per_cpu ret_stack that is used by the idle task. When we call
    ftrace_graph_init_idle_task() it will check if the idle task's
    ret_stack is NULL, if it is, then it will assign it the per_cpu
    Reported-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    Suggested-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Stable Tree <stable@kernel.org>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>