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Subject[PATCH 4.19 08/41] sched, trace: Fix prev_state output in sched_switch tracepoint
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pavankumar Kondeti <pkondeti@codeaurora.org>

commit 3054426dc68e5d63aa6a6e9b91ac4ec78e3f3805 upstream.

commit 3f5fe9fef5b2 ("sched/debug: Fix task state recording/printout")
tried to fix the problem introduced by a previous commit efb40f588b43
("sched/tracing: Fix trace_sched_switch task-state printing"). However
the prev_state output in sched_switch is still broken.

task_state_index() uses fls() which considers the LSB as 1. Left
shifting 1 by this value gives an incorrect mapping to the task state.
Fix this by decrementing the value returned by __get_task_state()
before shifting.

Link: http://lkml.kernel.org/r/1540882473-1103-1-git-send-email-pkondeti@codeaurora.org

Cc: stable@vger.kernel.org
Fixes: 3f5fe9fef5b2 ("sched/debug: Fix task state recording/printout")
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/trace/events/sched.h | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -107,6 +107,8 @@ DEFINE_EVENT(sched_wakeup_template, sche
#ifdef CREATE_TRACE_POINTS
static inline long __trace_sched_switch_state(bool preempt, struct task_struct *p)
{
+ unsigned int state;
+
#ifdef CONFIG_SCHED_DEBUG
BUG_ON(p != current);
#endif /* CONFIG_SCHED_DEBUG */
@@ -118,7 +120,15 @@ static inline long __trace_sched_switch_
if (preempt)
return TASK_REPORT_MAX;

- return 1 << task_state_index(p);
+ /*
+ * task_state_index() uses fls() and returns a value from 0-8 range.
+ * Decrement it by 1 (except TASK_RUNNING state i.e 0) before using
+ * it for left shift operation to get the correct task->state
+ * mapping.
+ */
+ state = task_state_index(p);
+
+ return state ? (1 << (state - 1)) : state;
}
#endif /* CREATE_TRACE_POINTS */


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