Re: [PATCH] arm64: use preempt_disable_notrace in _percpu_read/write

From: Catalin Marinas
Date: Fri Sep 09 2016 - 07:35:26 EST

On Thu, Sep 08, 2016 at 08:46:42PM +0800, Chunyan Zhang wrote:
> When debug preempt or preempt tracer is enabled, preempt_count_add/sub()
> can be traced by function and function graph tracing, and
> preempt_disable/enable() would call preempt_count_add/sub(), so in Ftrace
> subsystem we should use preempt_disable/enable_notrace instead.
> In the commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap
> like events do") the function this_cpu_read() was added to
> trace_graph_entry(), and if this_cpu_read() calls preempt_disable(), graph
> tracer will go into a recursive loop, even if the tracing_on is
> disabled.
> So this patch change to use preempt_enable/disable_notrace instead in
> this_cpu_read().
> Since Yonghui Yang helped a lot to find the root cause of this problem,
> so also add his SOB.
> Signed-off-by: Yonghui Yang <mark.yang@xxxxxxxxxxxxxx>
> Signed-off-by: Chunyan Zhang <zhang.chunyan@xxxxxxxxxx>

Queued for 4.8-rc6. Thanks.