Ankita Garg wrote:
On Tue, Jul 24, 2007 at 12:36:22PM +0200, John Sigler wrote:
Ankita Garg wrote:
This patch adds support to display captured -rt stats under
/proc/schedstat.
Signed-off-by: Ankita Garg <ankita@xxxxxxxxxx>
--
sched_stats.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
Index: linux-2.6.22.1/kernel/sched_stats.h
===================================================================
--- linux-2.6.22.1.orig/kernel/sched_stats.h 2007-07-23
18:15:57.000000000 +0530
+++ linux-2.6.22.1/kernel/sched_stats.h 2007-07-23
18:24:03.000000000 +0530
@@ -21,12 +21,15 @@
/* runqueue-specific stats */
seq_printf(seq,
- "cpu%d %lu %lu %lu %lu %lu %lu %lu %lu %lu %llu %llu
%lu",
+ "cpu%d %lu %lu %lu %lu %lu %lu %lu %lu %lu %llu %lu %lu
%lu %llu %lu",
cpu, rq->yld_both_empty,
rq->yld_act_empty, rq->yld_exp_empty, rq->yld_cnt,
rq->sched_switch, rq->sched_cnt, rq->sched_goidle,
rq->ttwu_cnt, rq->ttwu_local,
rq->rq_sched_info.cpu_time,
+#ifdef CONFIG_PREEMPT_RT
+ rq->rto_schedule, rq->rto_wakeup, rq->rto_pulled,
+#endif
rq->rq_sched_info.run_delay, rq->rq_sched_info.pcnt);
seq_printf(seq, "\n");
I know you've written a new patch that makes this one obsolete, but I
wanted to discuss this specific patch.
Originally, there were 13 conversion specifications, and your patch
adds 3, for a total of 16 conversion specifications.
However, if CONFIG_PREEMPT_RT is not defined, then seq_printf is
called with only 13 arguments.
Is it safe to call seq_printf with too few arguments?
So I tried to run the code disabling CONFIG_PREEMPT_RT, to see the
behavior vsnprintf() on supplying fewer arguments. Arbit/garbage value is
printed for conversion specifications that do not have a matching argument.
It did not cause any issue at all beyond that point. But considering the
correctness and quality of code, was going to post the updated patch (if
the re-work had not happened)!
I double-checked. Calling v*printf with too few parameters also leads to
undefined behavior.
You didn't notice any ill effects on your particular compiler / platform
combination, but the code above remains a time bomb :-)
Once in UB land, all bets are off.
Regards.
-
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