linux-kernel - Re: [PATCH] arm64: use preempt_disable_notrace in _percpu

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Date:   Fri, 9 Sep 2016 12:35:08 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Chunyan Zhang <zhang.chunyan@...aro.org>
Cc:     rostedt@...dmis.org, mingo@...hat.com, mark.yang@...eadtrum.com,
        zhang.lyra@...il.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, takahiro.akashi@...aro.org
Subject: Re: [PATCH] arm64: use preempt_disable_notrace in _percpu_read/write

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@...eadtrum.com>
> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>

Queued for 4.8-rc6. Thanks.

-- 
Catalin