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Subject[PATCH] [RFC]ARM: ftrace: pause/unpause function graph tracer in cpu_suspend()
Hi,all

On Mon, 4 Jan 2021 at 13:35, Louis Wang <liang26812@gmail.com> wrote:
>
> From: "louis.wang1" <louis.wang1@unisoc.com>
>
> Enabling function_graph tracer on ARM causes kernel panic, because the
> function graph tracer updates the "return address" of a function in order
> to insert a trace callback on function exit, it saves the function's
> original return address in a return trace stack, but cpu_suspend() may not
> return through the normal return path.
>
> cpu_suspend() will resume directly via the cpu_resume path, but the return
> trace stack has been set-up by the subfunctions of cpu_suspend(), which
> makes the "return address" inconsistent with cpu_suspend().
>
> This patch refers to Commit de818bd4522c40ea02a81b387d2fa86f989c9623
> ("arm64: kernel: pause/unpause function graph tracer in cpu_suspend()"),
> fixes the issue by pausing/resuming the function graph tracer on the thread
> executing cpu_suspend(), so that the function graph tracer state is kept
> consistent across functions that enter power down states and never return
> by effectively disabling graph tracer while they are executing.
>
> Signed-off-by: louis.wang1 <louis.wang1@unisoc.com>
> ---
> arch/arm/kernel/suspend.c | 19 ++++++++++++++++++-
> 1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/kernel/suspend.c b/arch/arm/kernel/suspend.c
> index 24bd205..43f0a3e 100644
> --- a/arch/arm/kernel/suspend.c
> +++ b/arch/arm/kernel/suspend.c
> @@ -1,4 +1,5 @@
> // SPDX-License-Identifier: GPL-2.0
> +#include <linux/ftrace.h>
> #include <linux/init.h>
> #include <linux/slab.h>
> #include <linux/mm_types.h>
> @@ -26,12 +27,22 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
> return -EINVAL;
>
> /*
> + * Function graph tracer state gets incosistent when the kernel
> + * calls functions that never return (aka suspend finishers) hence
> + * disable graph tracing during their execution.
> + */
> + pause_graph_tracing();
> +
> + /*
> * Provide a temporary page table with an identity mapping for
> * the MMU-enable code, required for resuming. On successful
> * resume (indicated by a zero return code), we need to switch
> * back to the correct page tables.
> */
> ret = __cpu_suspend(arg, fn, __mpidr);
> +
> + unpause_graph_tracing();
> +
> if (ret == 0) {
> cpu_switch_mm(mm->pgd, mm);
> local_flush_bp_all();
> @@ -45,7 +56,13 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
> int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
> {
> u32 __mpidr = cpu_logical_map(smp_processor_id());
> - return __cpu_suspend(arg, fn, __mpidr);
> + int ret;
> +
> + pause_graph_tracing();
> + ret = __cpu_suspend(arg, fn, __mpidr);
> + unpause_graph_tracing();
> +
> + return ret;
> }
> #define idmap_pgd NULL
> #endif
> --
> 2.7.4
>
ftrace function_graph tracer always cause kernel panic on my ARM device with
multiple CPUs, I found a solution for the problem on ARM64, refers to
the patch above,
I was wondering why this bugfix on ARM64 hasn't been upstreamed to ARM,
Does anyone have a similar problem and can share information with me?
Thanks.

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