linux-kernel - Re: [PATCH] tracing: Fix event filters and triggers to handle negative numbers

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Date:   Thu, 23 Aug 2018 20:48:49 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Al Viro <viro@...IV.linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix event filters and triggers to handle
 negative numbers

On Thu, 23 Aug 2018 13:25:34 +0300
Pavel Tikhomirov <ptikhomirov@...tuozzo.com> wrote:

> Then tracing syscall exit event it is extremely useful to filter exit
> codes equal to some negative value, to react only to required errors.
> But negative numbers does not work:
> 
> [root@...rch sys_exit_read]# echo "ret == -1" > filter
> bash: echo: write error: Invalid argument
> [root@...rch sys_exit_read]# cat filter
> ret == -1
>         ^
> parse_error: Invalid value (did you forget quotes)?

Thanks for the patch. I'll apply it and then start testing it!

-- Steve

> 
> Similar thing happens when setting triggers.
> 
> These is a regression in v4.17 introduced by the commit mentioned below,
> testing without these commit shows no problem with negative numbers.
> 
> Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
> Signed-off-by: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
> ---
>  kernel/trace/trace_events_filter.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 84a65173b1e9..2ba449292561 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -1299,7 +1299,7 @@ static int parse_pred(const char *str, void *data,
>  		/* go past the last quote */
>  		i++;
>  
> -	} else if (isdigit(str[i])) {
> +	} else if (isdigit(str[i]) || str[i] == '-') {
>  
>  		/* Make sure the field is not a string */
>  		if (is_string_field(field)) {
> @@ -1312,6 +1312,9 @@ static int parse_pred(const char *str, void *data,
>  			goto err_free;
>  		}
>  
> +		if (str[i] == '-')
> +			i++;
> +
>  		/* We allow 0xDEADBEEF */
>  		while (isalnum(str[i]))
>  			i++;