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SubjectRe: trace: fix multiple use of __print_flags and __print_symbolic
Steven Whitehouse wrote:
> When using multiple calls to __print_symbolic and __print_flags in
> the same tracer, I noticed that the output was incorrect. I think
> the following patch is the correct fix (it works for me) but please
> check it carefully since I'm not that familiar with this code,
> and I may well have made a mistake somewhere.
>

I don't see there's bug in __print_symbolic() or __print_flags():

enum print_line_t
ftrace_raw_output_##call(struct trace_iterator *iter, int flags)
{
...
p = &get_cpu_var(ftrace_event_seq);
/* here we call ftrace_print_flags_seq(p, ...) */
ret = trace_seq_printf(s, #call ": " print);
put_cpu();
...
}

ftrace_event_seq is percpu data, and here is used with preempt-disabled,
so there shouldn't be problem of concurrent accessing.


> The patch is vs. the latest -tip tree which doesn't yet seem to
> contain the EXPORT_SYMBOL() fix that I sent earlier.
>
> Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
>
>
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index c12d95d..ac6ced1 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -222,10 +222,9 @@ ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
> {
> unsigned long mask;
> const char *str;
> + const char *ret = p->buffer + p->len;
> int i;
>
> - trace_seq_init(p);
> -

This is wrong. Without reseting, the seq buffer will quickly be filled.

> for (i = 0; flag_array[i].name && flags; i++) {
>
> mask = flag_array[i].mask;
> @@ -248,7 +247,7 @@ ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
>
> trace_seq_putc(p, 0);
>
> - return p->buffer;
> + return ret;
> }
>
> const char *
> @@ -256,8 +255,7 @@ ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
> const struct trace_print_flags *symbol_array)
> {
> int i;
> -
> - trace_seq_init(p);
> + const char *ret = p->buffer + p->len;
>
> for (i = 0; symbol_array[i].name; i++) {
>
> @@ -273,7 +271,7 @@ ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
>
> trace_seq_putc(p, 0);
>
> - return p->buffer;
> + return ret;
> }
>
> #ifdef CONFIG_KRETPROBES
>


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