[PATCH 2/3] powerpc/xmon: Disable and enable tracing command

[Naveen N. Rao]

On 2017/07/31 02:22PM, Breno Leitao wrote:
> If tracing is enabled and you get into xmon, the tracing buffer
> continues to be updated, causing possible loss of data due to buffer
> overflow and unnecessary tracing information coming from xmon functions.
> 
> This patch adds a new option that allows the tracing to be disabled and
> re-enabled from inside xmon.

How is this new option useful? In the next patch, you disable tracing by 
default -- in what scenario do you expect to have to re-enable tracing 
from within xmon?

> 
> Signed-off-by: Breno Leitao <leitao at debian.org>
> ---
>  arch/powerpc/xmon/xmon.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 0cbd910193fa..19276d2f2f25 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -89,6 +89,7 @@ static unsigned long nidump = 16;
>  static unsigned long ncsum = 4096;
>  static int termch;
>  static char tmpstr[128];
> +static char tracing_enabled = 1;
> 
>  static long bus_error_jmp[JMP_BUF_LEN];
>  static int catch_memory_errors;
> @@ -268,6 +269,7 @@ Commands:\n\
>    Sr #	read SPR #\n\
>    Sw #v write v to SPR #\n\
>    t	print backtrace\n\
> +  v	trace enable/disable\n\
>    x	exit monitor and recover\n\
>    X	exit monitor and don't recover\n"
>  #if defined(CONFIG_PPC64) && !defined(CONFIG_PPC_BOOK3E)
> @@ -983,6 +985,17 @@ cmds(struct pt_regs *excp)
>  		case 'x':
>  		case 'X':
>  			return cmd;
> +		case 'v':
> +			if (tracing_is_on()) {
> +				printk("Disabling tracing\n");
> +				tracing_enabled = 0;
> +				tracing_off();

This only disables trace buffer updates - ftrace (and all its callbacks, 
et al) remains active, which isn't desirable. Can you see if this works 
for you:
https://patchwork.ozlabs.org/patch/769611/

- Naveen