lkml.org 
[lkml]   [2008]   [Oct]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH -v2] ring-buffer: add paranoid checks for loops

* Steven Rostedt <rostedt@goodmis.org> wrote:

> + /*
> + * This should normally only loop twice. But because the
> + * start of the reader inserts an empty page, it causes
> + * a case where we will loop three times. There should be no
> + * reason to loop four times (that I know of).
> + */
> + if (unlikely(paranoid > 2)) {
> + RB_WARN_ON(cpu_buffer, 1);
> + reader = NULL;
> + goto out;
> + }
> + paranoid++;

ok, the explanations look nice now.

A small nit - the above comment suggests that looping 4 times is the
anomaly - still the test is for paranoid > 2 ?
> + int paranoid = 0;

another small nit: i'd suggest to rename 'paranoid' to 'nr_loops' or
'nr_iterations' or so. It is the _condition_ that signals paranoia,
not the variable in itself - making the current patch look a bit
weird.

> again:
> + /*
> + * We repeat when a timestamp is encountered. It is possible
> + * to get multiple timestamps from an interrupt entering just
> + * as one timestamp is about to be written. The max times
> + * that this can happen is the number of nested interrupts we
> + * can have. 10 should be more than enough.
> + */
> + if (unlikely(paranoid > 10)) {
> + RB_WARN_ON(cpu_buffer, 1);
> + return NULL;

s/10 should be more than enough/Nesting higher than 10 is clearly
anomalous/

> + /*
> + * We repeat when a timestamp is encountered. It is possible
> + * to get multiple timestamps from an interrupt entering just
> + * as one timestamp is about to be written. The max times
> + * that this can happen is the number of nested interrupts we
> + * can have. 10 should be more than enough.
> + */
> + if (unlikely(paranoid > 10)) {
> + RB_WARN_ON(cpu_buffer, 1);
> + return NULL;

ditto.

Ingo


\
 
 \ /
  Last update: 2008-10-31 10:41    [from the cache]
©2003-2011 Jasper Spaans