Re: [Patch 2/2] ksym_tracer:Handle machine stall when cat trace_pipe for ksym tracer

Frederic Weisbecker
2009-06-17T05:12:47Z

On Wed, Jun 17, 2009 at 04:35:27AM +0530, K.Prasad wrote:
> 'trace_pipe' does not handle a TRACE_TYPE_PARTIAL_LINE well and causes the
> machine to stall.

No, if it stalls here, it means it handles it well :)

> While a TRACE_TYPE_UNHANDLED return causes the tracer to
> output unrelated data, a TRACE_TYPE_HANDLED return presents a clean output
> (minus all partial traces).
>
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
> kernel/trace/trace_ksym.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> Index: linux-2.6-tip.hbkpt/kernel/trace/trace_ksym.c
> ===================================================================
> --- linux-2.6-tip.hbkpt.orig/kernel/trace/trace_ksym.c
> +++ linux-2.6-tip.hbkpt/kernel/trace/trace_ksym.c
> @@ -389,6 +389,12 @@ static enum print_line_t ksym_trace_outp
>
> trace_assign_type(field, entry);
>
> + /*
> + * Return early without any output if we don't have sufficient
> + * information
> + */
> + if ((!field->ksym_hbp->info.type) || (!field->ip))
> + return TRACE_TYPE_HANDLED;

Yeah that seems a good fix. But such silent ignored traces may
hide bugs (current or futures).
Is it a common situation to have a zero ip or an undefined
breakpoint type? How can that happen?

Thanks.

> ret = trace_seq_printf(s, "%-15s %-5d %-3d %-20s ", field->p_name,
> entry->pid, iter->cpu, field->ksym_name);
> if (!ret) {
>