linux-kernel - Re: [PATCH] ARM: probes: Don't stop the machine if we're in the debugger

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Date:	Mon, 24 Aug 2015 17:19:26 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Douglas Anderson <dianders@...omium.org>
CC:	Kees Cook <keescook@...omium.org>, Nicolas Pitre <nico@...aro.org>,
	tixy@...aro.org, wangnan0@...wei.com, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org, Aapo Vienamo <avienamo@...dia.com>,
	rabin@....in, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: probes: Don't stop the machine if we're in the debugger

On 08/24/2015 04:58 PM, Douglas Anderson wrote:
> If we're in kgdb then the machine is already stopped.  Trying to stop
> it again will cause us to try to sleep, which is not allowed while in
> kgdb.  To avoid this problem, only stop the machine when we're not in
> kgdb.
>
> Reported-by: Aapo Vienamo <avienamo@...dia.com>
> Suggested-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---

Can you add the backtrace?

>   arch/arm/kernel/patch.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
> index 69bda1a..abf30ec 100644
> --- a/arch/arm/kernel/patch.c
> +++ b/arch/arm/kernel/patch.c
> @@ -1,5 +1,6 @@
>   #include <linux/kernel.h>
>   #include <linux/spinlock.h>
> +#include <linux/kgdb.h>
>   #include <linux/kprobes.h>
>   #include <linux/mm.h>
>   #include <linux/stop_machine.h>
> @@ -124,6 +125,9 @@ void __kprobes patch_text(void *addr, unsigned int insn)
>   		.insn = insn,
>   	};
>   
> -	stop_machine(patch_text_stop_machine, &patch, NULL);
> +	/* Stop machine before patching; but not if in the debugger */
> +	if (unlikely(in_dbg_master()))
> +		patch_text_stop_machine(&patch);
> +	else
> +		stop_machine(patch_text_stop_machine, &patch, NULL);
>   }

Perhaps it would be better to add a different function for the kgdb call 
site? Then it's explicit what's going on without us having to figure out 
when in_dbg_master() is true.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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