Re: Patch "arm64: kernel: pause/unpause function graph tracer in cpu_suspend()" has been added to the 4.1-stable tree

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

Hi Greg,

On Tue, Jan 26, 2016 at 10:54:50PM -0800, gregkh@linuxfoundation.org wrote:
> 
> This is a note to let you know that I've just added the patch titled
> 
>     arm64: kernel: pause/unpause function graph tracer in cpu_suspend()
> 
> to the 4.1-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      arm64-kernel-pause-unpause-function-graph-tracer-in-cpu_suspend.patch
> and it can be found in the queue-4.1 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

We have just noticed this patch did not make it to 3.18 stable kernel
even though it was marked for #3.16+, probably it has slipped through
the cracks, please let us know what we can do to get it applied
to the 3.18 stable tree.

Thanks !
Lorenzo

> 
> 
> From de818bd4522c40ea02a81b387d2fa86f989c9623 Mon Sep 17 00:00:00 2001
> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Date: Tue, 17 Nov 2015 11:50:51 +0000
> Subject: arm64: kernel: pause/unpause function graph tracer in cpu_suspend()
> 
> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> 
> commit de818bd4522c40ea02a81b387d2fa86f989c9623 upstream.
> 
> The function graph tracer adds instrumentation that is required to trace
> both entry and exit of a function. In particular the function graph
> tracer updates the "return address" of a function in order to insert
> a trace callback on function exit.
> 
> Kernel power management functions like cpu_suspend() are called
> upon power down entry with functions called "finishers" that are in turn
> called to trigger the power down sequence but they may not return to the
> kernel through the normal return path.
> 
> When the core resumes from low-power it returns to the cpu_suspend()
> function through the cpu_resume path, which leaves the trace stack frame
> set-up by the function tracer in an incosistent state upon return to the
> kernel when tracing is enabled.
> 
> This patch fixes the issue by pausing/resuming the function graph
> tracer on the thread executing cpu_suspend() (ie the function call that
> subsequently triggers the "suspend finishers"), 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.
> 
> Fixes: 819e50e25d0c ("arm64: Add ftrace support")
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Reported-by: Catalin Marinas <catalin.marinas@arm.com>
> Reported-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Acked-by: Steven Rostedt <rostedt@goodmis.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> ---
>  arch/arm64/kernel/suspend.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> --- a/arch/arm64/kernel/suspend.c
> +++ b/arch/arm64/kernel/suspend.c
> @@ -1,3 +1,4 @@
> +#include <linux/ftrace.h>
>  #include <linux/percpu.h>
>  #include <linux/slab.h>
>  #include <asm/cacheflush.h>
> @@ -71,6 +72,13 @@ int cpu_suspend(unsigned long arg, int (
>  	local_dbg_save(flags);
>  
>  	/*
> +	 * 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();
> +
> +	/*
>  	 * mm context saved on the stack, it will be restored when
>  	 * the cpu comes out of reset through the identity mapped
>  	 * page tables, so that the thread address space is properly
> @@ -111,6 +119,8 @@ int cpu_suspend(unsigned long arg, int (
>  			hw_breakpoint_restore(NULL);
>  	}
>  
> +	unpause_graph_tracing();
> +
>  	/*
>  	 * Restore pstate flags. OS lock and mdscr have been already
>  	 * restored, so from this point onwards, debugging is fully
> 
> 
> Patches currently in stable-queue which might be from lorenzo.pieralisi@arm.com are
> 
> queue-4.1/arm64-kernel-pause-unpause-function-graph-tracer-in-cpu_suspend.patch
>