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SubjectRe: [PATCH 1/5] ftrace: limit use of check pages
On Thu, 22 May 2008 00:22:16 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> The check_pages function is called often enough that it can cause problems
> with trace outputs or even bringing the system to a halt.
>
> This patch limits the check_pages to the places that are most likely to
> have problems. The check is made at the flip between the global array and
> the max save array, as well as when the size of the buffers changes and
> the self tests.
>
> This patch also removes the BUG_ON from check_pages and replaces it with
> a WARN_ON and disabling of the tracer.
>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
> kernel/trace/trace.c | 32 +++++++++++++++++++++++---------
> kernel/trace/trace_selftest.c | 1 +
> 2 files changed, 24 insertions(+), 9 deletions(-)
>
> Index: linux-tip.git/kernel/trace/trace.c
> ===================================================================
> --- linux-tip.git.orig/kernel/trace/trace.c 2008-05-21 13:25:34.000000000 -0400
> +++ linux-tip.git/kernel/trace/trace.c 2008-05-21 21:32:23.000000000 -0400
> @@ -249,24 +249,32 @@ __update_max_tr(struct trace_array *tr,
> tracing_record_cmdline(current);
> }
>
> +#define CHECK_COND(cond) \
> + if (unlikely(cond)) { \
> + tracing_disabled = 0; \

-----------------------------------^
This looks like a typo.
I also quickly read through the other patches and didn't see any
obvious problems in them.

> + WARN_ON(1); \
> + return -1; \
> + }
> +
> /**
> * check_pages - integrity check of trace buffers
> *
> * As a safty measure we check to make sure the data pages have not
> - * been corrupted. TODO: configure to disable this because it adds
> - * a bit of overhead.
> + * been corrupted.
> */
> -void check_pages(struct trace_array_cpu *data)
> +int check_pages(struct trace_array_cpu *data)
> {
> struct page *page, *tmp;
>
> - BUG_ON(data->trace_pages.next->prev != &data->trace_pages);
> - BUG_ON(data->trace_pages.prev->next != &data->trace_pages);
> + CHECK_COND(data->trace_pages.next->prev != &data->trace_pages);
> + CHECK_COND(data->trace_pages.prev->next != &data->trace_pages);
>
> list_for_each_entry_safe(page, tmp, &data->trace_pages, lru) {
> - BUG_ON(page->lru.next->prev != &page->lru);
> - BUG_ON(page->lru.prev->next != &page->lru);
> + CHECK_COND(page->lru.next->prev != &page->lru);
> + CHECK_COND(page->lru.prev->next != &page->lru);
> }
> +
> + return 0;
> }


--
Pekka Paalanen
http://www.iki.fi/pq/


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