Re: [PATCH 2/2] MIPS: Fix kernel hang under FUNCTION_GRAPH_TRACER and PREEMPT_TRACER

[Thomas Bogendoerfer]

On Sat, May 15, 2021 at 07:02:01PM +0800, Tiezhu Yang wrote:
> When update the latest mainline kernel with the following three configs,
> the kernel hangs during startup:
> 
> (1) CONFIG_FUNCTION_GRAPH_TRACER=y
> (2) CONFIG_PREEMPT_TRACER=y
> (3) CONFIG_FTRACE_STARTUP_TEST=y
> 
> When update the latest mainline kernel with the above two configs (1)
> and (2), the kernel starts normally, but it still hangs when execute
> the following command:
> 
> echo "function_graph" > /sys/kernel/debug/tracing/current_tracer
> 
> Without CONFIG_PREEMPT_TRACER=y, the above two kinds of kernel hangs
> disappeared, so it seems that CONFIG_PREEMPT_TRACER has some influences
> with function_graph tracer at the first glance.
> 
> I use ejtag to find out the epc address is related with preempt_enable()
> in the file arch/mips/lib/mips-atomic.c, because function tracing can
> trace the preempt_{enable,disable} calls that are traced, replace them
> with preempt_{enable,disable}_notrace to prevent function tracing from
> going into an infinite loop, and then it can fix the kernel hang issue.
> 
> By the way, it seems that this commit is a complement and improvement of
> commit f93a1a00f2bd ("MIPS: Fix crash that occurs when function tracing
> is enabled").
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> ---
>  arch/mips/lib/mips-atomic.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)

applied to mips-fixes.

Thomas.

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