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[PATCH v2 1/2] sched/debug: fix /proc/sched_debug regression

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Commit cb2517653fcc ("sched/debug: Make schedstats a runtime tunable
that is disabled by default") introduced a bug when CONFIG_SCHEDSTATS is
enabled and the runtime tunable is disabled (which is the default).  The
wait-time, sum-exec, and sum-sleep fields are missing from the
/proc/sched_debug file in the runnable_tasks section.

Fix it with a new schedstat_val() macro which returns the field value
when schedstats is enabled and zero otherwise.  The macro works with
both SCHEDSTATS and !SCHEDSTATS.  I put the macro in stats.h since it
might end up being useful in other places.

Fixes: cb2517653fcc ("sched/debug: Make schedstats a runtime tunable that is disabled by default")
Cc: stable@vger.kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 kernel/sched/debug.c | 15 ++++-----------
 kernel/sched/stats.h |  3 +++
 2 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index cf905f6..0368c39 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -427,19 +427,12 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 		SPLIT_NS(p->se.vruntime),
 		(long long)(p->nvcsw + p->nivcsw),
 		p->prio);
-#ifdef CONFIG_SCHEDSTATS
-	if (schedstat_enabled()) {
-		SEQ_printf(m, "%9Ld.%06ld %9Ld.%06ld %9Ld.%06ld",
-			SPLIT_NS(p->se.statistics.wait_sum),
-			SPLIT_NS(p->se.sum_exec_runtime),
-			SPLIT_NS(p->se.statistics.sum_sleep_runtime));
-	}
-#else
+
 	SEQ_printf(m, "%9Ld.%06ld %9Ld.%06ld %9Ld.%06ld",
-		0LL, 0L,
+		SPLIT_NS(schedstat_val(p, se.statistics.wait_sum)),
 		SPLIT_NS(p->se.sum_exec_runtime),
-		0LL, 0L);
-#endif
+		SPLIT_NS(schedstat_val(p, se.statistics.sum_sleep_runtime)));
+
 #ifdef CONFIG_NUMA_BALANCING
 	SEQ_printf(m, " %d %d", task_node(p), task_numa_group_id(p));
 #endif
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 70b3b6a..78955cb 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -33,6 +33,8 @@ rq_sched_info_dequeued(struct rq *rq, unsigned long long delta)
 # define schedstat_inc(rq, field)	do { if (schedstat_enabled()) { (rq)->field++; } } while (0)
 # define schedstat_add(rq, field, amt)	do { if (schedstat_enabled()) { (rq)->field += (amt); } } while (0)
 # define schedstat_set(var, val)	do { if (schedstat_enabled()) { var = (val); } } while (0)
+# define schedstat_val(rq, field)	((schedstat_enabled()) ? (rq)->field : 0)
+
 #else /* !CONFIG_SCHEDSTATS */
 static inline void
 rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
@@ -47,6 +49,7 @@ rq_sched_info_depart(struct rq *rq, unsigned long long delta)
 # define schedstat_inc(rq, field)	do { } while (0)
 # define schedstat_add(rq, field, amt)	do { } while (0)
 # define schedstat_set(var, val)	do { } while (0)
+# define schedstat_val(rq, field)	0
 #endif
 
 #ifdef CONFIG_SCHED_INFO
-- 
2.4.11

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[PATCH v2 1/2] sched/debug: fix /proc/sched_debug regression Josh Poimboeuf <jpoimboe@redhat.com> - 2016-06-04 01:00 +0200
  Re: [PATCH v2 1/2] sched/debug: fix /proc/sched_debug regression Mel Gorman <mgorman@techsingularity.net> - 2016-06-07 15:50 +0200
    Re: [PATCH v2 1/2] sched/debug: fix /proc/sched_debug regression Josh Poimboeuf <jpoimboe@redhat.com> - 2016-06-07 20:00 +0200
  [tip:sched/core] sched/debug: Fix /proc/sched_debug regression tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-06-08 16:30 +0200

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