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sched/tracing: Don't re-read p->state when emitting sched_switch event

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  c6e7bd7afa ("sched/core: Optimize ttwu() spinning on p->on_cpu")

the following sequence becomes possible:

		      p->__state = TASK_INTERRUPTIBLE;
		      __schedule()
			deactivate_task(p);
  ttwu()
    READ !p->on_rq
    p->__state=TASK_WAKING
			trace_sched_switch()
			  __trace_sched_switch_state()
			    task_state_index()
			      return 0;

TASK_WAKING isn't in TASK_REPORT, so the task appears as TASK_RUNNING in
the trace event.

Prevent this by pushing the value read from __schedule() down the trace
event.

Reported-by: Abhijeet Dharmapurikar <adharmap@quicinc.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20220120162520.570782-2-valentin.schneider@arm.com
This commit is contained in:
Valentin Schneider 2022-01-20 16:25:19 +00:00 • committed by Peter Zijlstra
parent 49bef33e4b
commit fa2c3254d7
9 changed files with 34 additions and 14 deletions
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4
kernel/trace/fgraph.c
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@ -415,7 +415,9 @@ free:
static void
ftrace_graph_probe_sched_switch(void *ignore, bool preempt,
struct task_struct *prev, struct task_struct *next)
unsigned int prev_state,
struct task_struct *prev,
struct task_struct *next)
{
unsigned long long timestamp;
int index;