Re: [Patch 1/2] ksym_tracer:Fix line-wrapping after removal of ksym tracer entry

Frederic Weisbecker
2009-06-17T05:06:24Z

On Wed, Jun 17, 2009 at 04:35:04AM +0530, K.Prasad wrote:
> Removal of a ksym entry results in missing information and an early return with
> TRACE_TYPE_PARTIAL_LINE code (minus the line return). This patch modifies the
> output function to unconditionally add a line return irrespective of the
> return code.
>
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
> kernel/trace/trace_ksym.c | 27 +++++++++++++++------------
> 1 file changed, 15 insertions(+), 12 deletions(-)
>
> 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
> @@ -391,29 +391,32 @@ static enum print_line_t ksym_trace_outp
>
> ret = trace_seq_printf(s, "%-15s %-5d %-3d %-20s ", field->p_name,
> entry->pid, iter->cpu, field->ksym_name);
> - if (!ret)
> - return TRACE_TYPE_PARTIAL_LINE;
> + if (!ret) {
> + ret = TRACE_TYPE_PARTIAL_LINE;
> + goto err_ret;
> + }
>
> + ret = TRACE_TYPE_PARTIAL_LINE;
> switch (field->ksym_hbp->info.type) {
> case HW_BREAKPOINT_WRITE:
> - ret = trace_seq_printf(s, " W ");
> + if (!trace_seq_printf(s, " W "))
> + goto err_ret;
> break;
> case HW_BREAKPOINT_RW:
> - ret = trace_seq_printf(s, " RW ");
> + if (!trace_seq_printf(s, " RW "))
> + goto err_ret;
> break;
> default:
> - return TRACE_TYPE_PARTIAL_LINE;
> + goto err_ret;
> }
>
> - if (!ret)
> - return TRACE_TYPE_PARTIAL_LINE;
> -
> sprint_symbol(str, field->ip);
> ret = trace_seq_printf(s, "%-20s\n", str);
> - if (!ret)
> - return TRACE_TYPE_PARTIAL_LINE;
> -
> - return TRACE_TYPE_HANDLED;
> + if (ret)
> + return TRACE_TYPE_HANDLED;
> +err_ret:
> + trace_seq_printf(s, "\n");
> + return ret;

As told in my email just before, TRACE_TYPE_PARTIAL_LINE
won't print a truncated line or a partial line. Instead, it
will be ignored and entirely retried later.
Then your newline will be ignored.

..unless we have a bug in trace.c

I'm not sure what it the origin of the concatenated printed entries
Ingo has reported.

Did you reproduce it and then this patch fixed it?

> }
>
> struct tracer ksym_tracer __read_mostly =
>