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

From: tip-bot2 for Valentin Schneider
Date: Tue Mar 01 2022 - 10:24:49 EST

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The following commit has been merged into the sched/core branch of tip:

Commit-ID: fa2c3254d7cfff5f7a916ab928a562d1165f17bb
Gitweb: https://git.kernel.org/tip/fa2c3254d7cfff5f7a916ab928a562d1165f17bb
Author: Valentin Schneider <valentin.schneider@xxxxxxx>
AuthorDate: Thu, 20 Jan 2022 16:25:19
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 01 Mar 2022 16:18:39 +01:00

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

As of commit

c6e7bd7afaeb ("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@xxxxxxxxxxx>
Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220120162520.570782-2-valentin.schneider@xxxxxxx
---
include/linux/sched.h | 11 ++++++++---
include/trace/events/sched.h | 11 +++++++----
kernel/sched/core.c | 4 ++--
kernel/trace/fgraph.c | 4 +++-
kernel/trace/ftrace.c | 4 +++-
kernel/trace/trace_events.c | 8 ++++++--
kernel/trace/trace_osnoise.c | 4 +++-
kernel/trace/trace_sched_switch.c | 1 +
kernel/trace/trace_sched_wakeup.c | 1 +
9 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f00132e..457c8a0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1620,10 +1620,10 @@ static inline pid_t task_pgrp_nr(struct task_struct *tsk)
#define TASK_REPORT_IDLE (TASK_REPORT + 1)
#define TASK_REPORT_MAX (TASK_REPORT_IDLE << 1)

-static inline unsigned int task_state_index(struct task_struct *tsk)
+static inline unsigned int __task_state_index(unsigned int tsk_state,
+ unsigned int tsk_exit_state)
{
- unsigned int tsk_state = READ_ONCE(tsk->__state);
- unsigned int state = (tsk_state | tsk->exit_state) & TASK_REPORT;
+ unsigned int state = (tsk_state | tsk_exit_state) & TASK_REPORT;

BUILD_BUG_ON_NOT_POWER_OF_2(TASK_REPORT_MAX);

@@ -1633,6 +1633,11 @@ static inline unsigned int task_state_index(struct task_struct *tsk)
return fls(state);
}

+static inline unsigned int task_state_index(struct task_struct *tsk)
+{
+ return __task_state_index(READ_ONCE(tsk->__state), tsk->exit_state);
+}
+
static inline char task_index_to_char(unsigned int state)
{
static const char state_char[] = "RSDTtXZPI";
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 9464048..65e7867 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -187,7 +187,9 @@ DEFINE_EVENT(sched_wakeup_template, sched_wakeup_new,
TP_ARGS(p));

#ifdef CREATE_TRACE_POINTS
-static inline long __trace_sched_switch_state(bool preempt, struct task_struct *p)
+static inline long __trace_sched_switch_state(bool preempt,
+ unsigned int prev_state,
+ struct task_struct *p)
{
unsigned int state;

@@ -208,7 +210,7 @@ static inline long __trace_sched_switch_state(bool preempt, struct task_struct *
* it for left shift operation to get the correct task->state
* mapping.
*/
- state = task_state_index(p);
+ state = __task_state_index(prev_state, p->exit_state);

return state ? (1 << (state - 1)) : state;
}
@@ -220,10 +222,11 @@ static inline long __trace_sched_switch_state(bool preempt, struct task_struct *
TRACE_EVENT(sched_switch,

TP_PROTO(bool preempt,
+ unsigned int prev_state,
struct task_struct *prev,
struct task_struct *next),

- TP_ARGS(preempt, prev, next),
+ TP_ARGS(preempt, prev_state, prev, next),

TP_STRUCT__entry(
__array( char, prev_comm, TASK_COMM_LEN )
@@ -239,7 +242,7 @@ TRACE_EVENT(sched_switch,
memcpy(__entry->next_comm, next->comm, TASK_COMM_LEN);
__entry->prev_pid = prev->pid;
__entry->prev_prio = prev->prio;
- __entry->prev_state = __trace_sched_switch_state(preempt, prev);
+ __entry->prev_state = __trace_sched_switch_state(preempt, prev_state, prev);
memcpy(__entry->prev_comm, prev->comm, TASK_COMM_LEN);
__entry->next_pid = next->pid;
__entry->next_prio = next->prio;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ef94612..3aafc15 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4836,7 +4836,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
{
struct rq *rq = this_rq();
struct mm_struct *mm = rq->prev_mm;
- long prev_state;
+ unsigned int prev_state;

/*
* The previous task will have left us with a preempt_count of 2
@@ -6300,7 +6300,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
migrate_disable_switch(rq, prev);
psi_sched_switch(prev, next, !task_on_rq_queued(prev));

- trace_sched_switch(sched_mode & SM_MASK_PREEMPT, prev, next);
+ trace_sched_switch(sched_mode & SM_MASK_PREEMPT, prev_state, prev, next);

/* Also unlocks the rq: */
rq = context_switch(rq, prev, next, &rf);
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 22061d3..19028e0 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -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;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index f9feb19..6762ae0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7347,7 +7347,9 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops)

static void
ftrace_filter_pid_sched_switch_probe(void *data, bool preempt,
- struct task_struct *prev, struct task_struct *next)
+ unsigned int prev_state,
+ struct task_struct *prev,
+ struct task_struct *next)
{
struct trace_array *tr = data;
struct trace_pid_list *pid_list;
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 3147614..2a19ea7 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -759,7 +759,9 @@ void trace_event_follow_fork(struct trace_array *tr, bool enable)

static void
event_filter_pid_sched_switch_probe_pre(void *data, bool preempt,
- struct task_struct *prev, struct task_struct *next)
+ unsigned int prev_state,
+ struct task_struct *prev,
+ struct task_struct *next)
{
struct trace_array *tr = data;
struct trace_pid_list *no_pid_list;
@@ -783,7 +785,9 @@ event_filter_pid_sched_switch_probe_pre(void *data, bool preempt,

static void
event_filter_pid_sched_switch_probe_post(void *data, bool preempt,
- struct task_struct *prev, struct task_struct *next)
+ unsigned int prev_state,
+ struct task_struct *prev,
+ struct task_struct *next)
{
struct trace_array *tr = data;
struct trace_pid_list *no_pid_list;
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 870a08d..1829b4c 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1167,7 +1167,9 @@ thread_exit(struct osnoise_variables *osn_var, struct task_struct *t)
* used to record the beginning and to report the end of a thread noise window.
*/
static void
-trace_sched_switch_callback(void *data, bool preempt, struct task_struct *p,
+trace_sched_switch_callback(void *data, bool preempt,
+ unsigned int prev_state,
+ struct task_struct *p,
struct task_struct *n)
{
struct osnoise_variables *osn_var = this_cpu_osn_var();
diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index e304196..993b0ed 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -22,6 +22,7 @@ static DEFINE_MUTEX(sched_register_mutex);

static void
probe_sched_switch(void *ignore, bool preempt,
+ unsigned int prev_state,
struct task_struct *prev, struct task_struct *next)
{
int flags;
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 2402de5..46429f9 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -426,6 +426,7 @@ tracing_sched_wakeup_trace(struct trace_array *tr,

static void notrace
probe_wakeup_sched_switch(void *ignore, bool preempt,
+ unsigned int prev_state,
struct task_struct *prev, struct task_struct *next)
{
struct trace_array_cpu *data;

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