v2 Documentation and rcutorture changes for 3.9

PATCH In review Paul E. McKenney 2 participants 7 messages Jan 27, 2013 – Jan 29, 2013

Subsystems (6)

Documentation Library code Tracing RCU +2 more subsystems

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Paul E. McKenney

author

2013-01-27 00:04 UTC #0 lore raw

cover v2 Documentation and rcutorture changes for 3.9

Hello!

The following are changes to documentation and rcutorture:

1. Export trace_clock_local() in order to allow rcutorture event
tracing to emit the time of the beginning of the RCU read-side critical section at the point where a failure is detected.
2. Reduce rcutorture's read-side tracing to include only failures,
thus cutting the number of events down to something reasonable (normally zero, in fact!).
3. Add atomic_xchg() to the list of atomic operations and memory
barriers, courtesy of Richard Braun.
4. Make rcutorture's shuffler task also shuffle recently added
rcutorture kthreads.

Changes since v1:

o Fixed build problem in #2 located by Randy Dunlap based on
diagnosis from Steven Rostedt.

o Added patch #4.

Thanx, Paul

 b/Documentation/atomic_ops.txt      |    2 +
 b/Documentation/memory-barriers.txt |    1 
 b/include/linux/rcupdate.h          |   13 ++++++--
 b/include/trace/events/rcu.h        |   19 +++++++++---
 b/kernel/rcupdate.c                 |    9 +++--
 b/kernel/rcutorture.c               |   55 ++++++++++++++++++++++++++++--------
 b/kernel/trace/trace_clock.c        |    1 
 b/lib/Kconfig.debug                 |    1 
 8 files changed, 79 insertions(+), 22 deletions(-)

Paul E. McKenney

author

2013-01-27 00:05 UTC #1 lore raw

PATCH 1/4 tracing: Export trace_clock_local()

From: "Paul E. McKenney" <[email protected]>

The rcutorture tests need to be able to trace the time of the beginning of an RCU read-side critical section, and thus need access to trace_clock_local(). This commit therefore adds a the needed EXPORT_SYMBOL_GPL().

Signed-off-by Paul E. McKenney <[email protected]>

Reviewed-by Josh Triplett <[email protected]>

---
 kernel/trace/trace_clock.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

kernel/trace/trace_clock.c +1 -0

index 3947835..1bbb1b2 100644
@@ -44,6 +44,7 @@ u64 notrace trace_clock_local(void)
 
 	return clock;
 }
+EXPORT_SYMBOL_GPL(trace_clock_local);
 
 /*
  * trace_clock(): 'between' trace clock. Not completely serialized,

Signature · 1 line

1.7.8

Paul E. McKenney

author

2013-01-27 00:05 UTC #4 lore raw

PATCH 4/4 rcu: Make rcutorture's shuffler task shuffle recently added tasks

From: "Paul E. McKenney" <[email protected]>

A number of kthreads have been added to rcutorture, but the shuffler task was not informed of them, and thus did not shuffle them. This commit therefore adds the requisite shuffling.

Signed-off-by Paul E. McKenney <[email protected]>

---
 kernel/rcutorture.c |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

kernel/rcutorture.c +20 -4

index a583f1c..3ebc8bf 100644
@@ -846,7 +846,7 @@ static int rcu_torture_boost(void *arg)
 		/* Wait for the next test interval. */
 		oldstarttime = boost_starttime;
 		while (ULONG_CMP_LT(jiffies, oldstarttime)) {
-			schedule_timeout_uninterruptible(1);
+			schedule_timeout_interruptible(oldstarttime - jiffies);
 			rcu_stutter_wait("rcu_torture_boost");
 			if (kthread_should_stop() ||
 			    fullstop != FULLSTOP_DONTSTOP)

@@ -1318,19 +1318,35 @@ static void rcu_torture_shuffle_tasks(void)
 				set_cpus_allowed_ptr(reader_tasks[i],
 						     shuffle_tmp_mask);
 	}
-
 	if (fakewriter_tasks) {
 		for (i = 0; i < nfakewriters; i++)
 			if (fakewriter_tasks[i])
 				set_cpus_allowed_ptr(fakewriter_tasks[i],
 						     shuffle_tmp_mask);
 	}
-
 	if (writer_task)
 		set_cpus_allowed_ptr(writer_task, shuffle_tmp_mask);
-
 	if (stats_task)
 		set_cpus_allowed_ptr(stats_task, shuffle_tmp_mask);
+	if (stutter_task)
+		set_cpus_allowed_ptr(stutter_task, shuffle_tmp_mask);
+	if (fqs_task)
+		set_cpus_allowed_ptr(fqs_task, shuffle_tmp_mask);
+	if (shutdown_task)
+		set_cpus_allowed_ptr(shutdown_task, shuffle_tmp_mask);
+#ifdef CONFIG_HOTPLUG_CPU
+	if (onoff_task)
+		set_cpus_allowed_ptr(onoff_task, shuffle_tmp_mask);
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+	if (stall_task)
+		set_cpus_allowed_ptr(stall_task, shuffle_tmp_mask);
+	if (barrier_cbs_tasks)
+		for (i = 0; i < n_barrier_cbs; i++)
+			if (barrier_cbs_tasks[i])
+				set_cpus_allowed_ptr(barrier_cbs_tasks[i],
+						     shuffle_tmp_mask);
+	if (barrier_task)
+		set_cpus_allowed_ptr(barrier_task, shuffle_tmp_mask);
 
 	if (rcu_idle_cpu == -1)
 		rcu_idle_cpu = num_online_cpus() - 1;

Signature · 1 line

1.7.8

Paul E. McKenney

author

2013-01-27 00:05 UTC #3 lore raw

PATCH 3/4 Documentation: Memory barrier semantics of atomic_xchg()

In reply to Paul E. McKenney

From: Richard Braun <[email protected]>

Add atomic_xchg() to documentation for atomic operations and memory barriers.

Signed-off-by Richard Braun <[email protected]>

Signed-off-by Paul E. McKenney <[email protected]>

Reviewed-by Josh Triplett <[email protected]>

---
 Documentation/atomic_ops.txt      |    2 ++
 Documentation/memory-barriers.txt |    1 +
 2 files changed, 3 insertions(+), 0 deletions(-)

Documentation/atomic_ops.txt +2 -0

index 27f2b21..d9ca5be 100644
@@ -253,6 +253,8 @@ This performs an atomic exchange operation on the atomic variable v, setting
 the given new value.  It returns the old value that the atomic variable v had
 just before the operation.
 
+atomic_xchg requires explicit memory barriers around the operation.
+
 	int atomic_cmpxchg(atomic_t *v, int old, int new);
 
 This performs an atomic compare exchange operation on the atomic value v,

Documentation/memory-barriers.txt +1 -0

index 3c4e1b3..fa5d8a9 100644
@@ -1685,6 +1685,7 @@ explicit lock operations, described later).  These include:
 
 	xchg();
 	cmpxchg();
+	atomic_xchg();
 	atomic_cmpxchg();
 	atomic_inc_return();
 	atomic_dec_return();

Signature · 1 line

1.7.8

Paul E. McKenney

author

2013-01-27 00:22 UTC #2 lore raw

PATCH 2/4 rcu: Reduce rcutorture tracing

In reply to Paul E. McKenney

From: "Paul E. McKenney" <[email protected]>

Currently, rcutorture traces every read-side access. This can be problematic because even a two-minute rcutorture run on a two-CPU system can generate 28,853,363 reads. Normally, only a failing read is of interest, so this commit traces adjusts rcutorture's tracing to only trace failing reads. The resulting event tracing records the time and the ->completed value captured at the beginning of the RCU read-side critical section, allowing correlation with other event-tracing messages.

Signed-off-by Paul E. McKenney <[email protected]>

Reviewed-by Josh Triplett <[email protected]>

[ paulmck: Add fix to build problem located by Randy Dunlap based on
diagnosis by Steven Rostedt. ]

---
 include/linux/rcupdate.h   |   13 ++++++++++---
 include/trace/events/rcu.h |   19 ++++++++++++++-----
 kernel/rcupdate.c          |    9 ++++++---
 kernel/rcutorture.c        |   31 ++++++++++++++++++++++++-------
 lib/Kconfig.debug          |    1 +
 5 files changed, 55 insertions(+), 18 deletions(-)

include/linux/rcupdate.h +10 -3

index 275aa3f..7f89cea 100644
@@ -53,7 +53,10 @@ extern int rcutorture_runnable; /* for sysctl */
 extern void rcutorture_record_test_transition(void);
 extern void rcutorture_record_progress(unsigned long vernum);
 extern void do_trace_rcu_torture_read(char *rcutorturename,
-				      struct rcu_head *rhp);
+				      struct rcu_head *rhp,
+				      unsigned long secs,
+				      unsigned long c_old,
+				      unsigned long c);
 #else
 static inline void rcutorture_record_test_transition(void)
 {

@@ -63,9 +66,13 @@ static inline void rcutorture_record_progress(unsigned long vernum)
 }
 #ifdef CONFIG_RCU_TRACE
 extern void do_trace_rcu_torture_read(char *rcutorturename,
-				      struct rcu_head *rhp);
+				      struct rcu_head *rhp,
+				      unsigned long secs,
+				      unsigned long c_old,
+				      unsigned long c);
 #else
-#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
+#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
+	do { } while (0)
 #endif
 #endif

include/trace/events/rcu.h +14 -5

index d4f559b..09af021 100644
@@ -523,22 +523,30 @@ TRACE_EVENT(rcu_batch_end,
  */
 TRACE_EVENT(rcu_torture_read,
 
-	TP_PROTO(char *rcutorturename, struct rcu_head *rhp),
+	TP_PROTO(char *rcutorturename, struct rcu_head *rhp,
+		 unsigned long secs, unsigned long c_old, unsigned long c),
 
-	TP_ARGS(rcutorturename, rhp),
+	TP_ARGS(rcutorturename, rhp, secs, c_old, c),
 
 	TP_STRUCT__entry(
 		__field(char *, rcutorturename)
 		__field(struct rcu_head *, rhp)
+		__field(unsigned long, secs)
+		__field(unsigned long, c_old)
+		__field(unsigned long, c)
 	),
 
 	TP_fast_assign(
 		__entry->rcutorturename = rcutorturename;
 		__entry->rhp = rhp;
+		__entry->secs = secs;
+		__entry->c_old = c_old;
+		__entry->c = c;
 	),
 
-	TP_printk("%s torture read %p",
-		  __entry->rcutorturename, __entry->rhp)
+	TP_printk("%s torture read %p %luus c: %lu %lu",
+		  __entry->rcutorturename, __entry->rhp,
+		  __entry->secs, __entry->c_old, __entry->c)
 );
 
 /*

@@ -608,7 +616,8 @@ TRACE_EVENT(rcu_barrier,
 #define trace_rcu_invoke_kfree_callback(rcuname, rhp, offset) do { } while (0)
 #define trace_rcu_batch_end(rcuname, callbacks_invoked, cb, nr, iit, risk) \
 	do { } while (0)
-#define trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
+#define trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
+	do { } while (0)
 #define trace_rcu_barrier(name, s, cpu, cnt, done) do { } while (0)
 
 #endif /* #else #ifdef CONFIG_RCU_TRACE */

kernel/rcupdate.c +6 -3

index a2cf761..303359d 100644
@@ -404,11 +404,14 @@ EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
-void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
+void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,
+			       unsigned long secs,
+			       unsigned long c_old, unsigned long c)
 {
-	trace_rcu_torture_read(rcutorturename, rhp);
+	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
 }
 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 #else
-#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
+#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
+	do { } while (0)
 #endif

kernel/rcutorture.c +24 -7

index 31dea01..a583f1c 100644
@@ -46,6 +46,7 @@
 #include <linux/stat.h>
 #include <linux/srcu.h>
 #include <linux/slab.h>
+#include <linux/trace_clock.h>
 #include <asm/byteorder.h>
 
 MODULE_LICENSE("GPL");

@@ -1028,7 +1029,6 @@ void rcutorture_trace_dump(void)
 		return;
 	if (atomic_xchg(&beenhere, 1) != 0)
 		return;
-	do_trace_rcu_torture_read(cur_ops->name, (struct rcu_head *)~0UL);
 	ftrace_dump(DUMP_ALL);
 }

@@ -1042,13 +1042,16 @@ static void rcu_torture_timer(unsigned long unused)
 {
 	int idx;
 	int completed;
+	int completed_end;
 	static DEFINE_RCU_RANDOM(rand);
 	static DEFINE_SPINLOCK(rand_lock);
 	struct rcu_torture *p;
 	int pipe_count;
+	unsigned long long ts;
 
 	idx = cur_ops->readlock();
 	completed = cur_ops->completed();
+	ts = trace_clock_local();
 	p = rcu_dereference_check(rcu_torture_current,
 				  rcu_read_lock_bh_held() ||
 				  rcu_read_lock_sched_held() ||

@@ -1058,7 +1061,6 @@ static void rcu_torture_timer(unsigned long unused)
 		cur_ops->readunlock(idx);
 		return;
 	}
-	do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 	if (p->rtort_mbtest == 0)
 		atomic_inc(&n_rcu_torture_mberror);
 	spin_lock(&rand_lock);

@@ -1071,10 +1073,16 @@ static void rcu_torture_timer(unsigned long unused)
 		/* Should not happen, but... */
 		pipe_count = RCU_TORTURE_PIPE_LEN;
 	}
-	if (pipe_count > 1)
+	completed_end = cur_ops->completed();
+	if (pipe_count > 1) {
+		unsigned long __maybe_unused ts_rem = do_div(ts, NSEC_PER_USEC);
+
+		do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu, ts,
+					  completed, completed_end);
 		rcutorture_trace_dump();
+	}
 	__this_cpu_inc(rcu_torture_count[pipe_count]);
-	completed = cur_ops->completed() - completed;
+	completed = completed_end - completed;
 	if (completed > RCU_TORTURE_PIPE_LEN) {
 		/* Should not happen, but... */
 		completed = RCU_TORTURE_PIPE_LEN;

@@ -1094,11 +1102,13 @@ static int
 rcu_torture_reader(void *arg)
 {
 	int completed;
+	int completed_end;
 	int idx;
 	DEFINE_RCU_RANDOM(rand);
 	struct rcu_torture *p;
 	int pipe_count;
 	struct timer_list t;
+	unsigned long long ts;
 
 	VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
 	set_user_nice(current, 19);

@@ -1112,6 +1122,7 @@ rcu_torture_reader(void *arg)
 		}
 		idx = cur_ops->readlock();
 		completed = cur_ops->completed();
+		ts = trace_clock_local();
 		p = rcu_dereference_check(rcu_torture_current,
 					  rcu_read_lock_bh_held() ||
 					  rcu_read_lock_sched_held() ||

@@ -1122,7 +1133,6 @@ rcu_torture_reader(void *arg)
 			schedule_timeout_interruptible(HZ);
 			continue;
 		}
-		do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
 		if (p->rtort_mbtest == 0)
 			atomic_inc(&n_rcu_torture_mberror);
 		cur_ops->read_delay(&rand);

@@ -1132,10 +1142,17 @@ rcu_torture_reader(void *arg)
 			/* Should not happen, but... */
 			pipe_count = RCU_TORTURE_PIPE_LEN;
 		}
-		if (pipe_count > 1)
+		completed_end = cur_ops->completed();
+		if (pipe_count > 1) {
+			unsigned long __maybe_unused ts_rem =
+					do_div(ts, NSEC_PER_USEC);
+
+			do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu,
+						  ts, completed, completed_end);
 			rcutorture_trace_dump();
+		}
 		__this_cpu_inc(rcu_torture_count[pipe_count]);
-		completed = cur_ops->completed() - completed;
+		completed = completed_end - completed;
 		if (completed > RCU_TORTURE_PIPE_LEN) {
 			/* Should not happen, but... */
 			completed = RCU_TORTURE_PIPE_LEN;

lib/Kconfig.debug +1 -0

index 3a35309..7d83f52 100644
@@ -1008,6 +1008,7 @@ config RCU_CPU_STALL_INFO
 config RCU_TRACE
 	bool "Enable tracing for RCU"
 	depends on DEBUG_KERNEL
+	select TRACE_CLOCK
 	help
 	  This option provides tracing in RCU which presents stats
 	  in debugfs for debugging RCU implementation.

Signature · 1 line

1.7.8

Josh Triplett

maintainer

2013-01-27 10:48 UTC #5 lore raw

Re: [PATCH tip/core/rcu 4/4] rcu: Make rcutorture's shuffler task shuffle recently added tasks

In reply to Paul E. McKenney

Quoted 7 lines · Paul E. McKenney

From: "Paul E. McKenney" <[email protected]>
A number of kthreads have been added to rcutorture, but the shuffler task was not informed of them, and thus did not shuffle them. This commit therefore adds the requisite shuffling.
Signed-off-by Paul E. McKenney <[email protected]>

This also makes an unrelated semantic change, and several unrelated whitespace changes.

Quoted 9 lines

---
 kernel/rcutorture.c |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

kernel/rcutorture.c +0 -0

index a583f1c..3ebc8bf 100644

kernel/rcutorture.c static int rcu_torture_boost(void *arg) · line 849

Quoted 5 lines

kernel/rcutorture.c +1 -1

@@ -846,7 +846,7 @@ static int rcu_torture_boost(void *arg)
 		/* Wait for the next test interval. */
 		oldstarttime = boost_starttime;
 		while (ULONG_CMP_LT(jiffies, oldstarttime)) {
-			schedule_timeout_uninterruptible(1);
+			schedule_timeout_interruptible(oldstarttime - jiffies);

This change doesn't seem related, and the commit message doesn't explain it either. Could you split it out into a separate commit and document the rationale, please?

Quoted 8 lines

kernel/rcutorture.c +0 -1

 			rcu_stutter_wait("rcu_torture_boost");
 			if (kthread_should_stop() ||
 			    fullstop != FULLSTOP_DONTSTOP)

@@ -1318,19 +1318,35 @@ static void rcu_torture_shuffle_tasks(void)
 				set_cpus_allowed_ptr(reader_tasks[i],
 						     shuffle_tmp_mask);
 	}
-

kernel/rcutorture.c static void rcu_torture_shuffle_tasks(void) · line 1331

Quoted 10 lines

kernel/rcutorture.c +0 -2

 	if (fakewriter_tasks) {
 		for (i = 0; i < nfakewriters; i++)
 			if (fakewriter_tasks[i])
 				set_cpus_allowed_ptr(fakewriter_tasks[i],
 						     shuffle_tmp_mask);
 	}
-
 	if (writer_task)
 		set_cpus_allowed_ptr(writer_task, shuffle_tmp_mask);
-

These three whitespace changes seem unrelated as well.

Quoted 11 lines

kernel/rcutorture.c +9 -0

 	if (stats_task)
 		set_cpus_allowed_ptr(stats_task, shuffle_tmp_mask);
+	if (stutter_task)
+		set_cpus_allowed_ptr(stutter_task, shuffle_tmp_mask);
+	if (fqs_task)
+		set_cpus_allowed_ptr(fqs_task, shuffle_tmp_mask);
+	if (shutdown_task)
+		set_cpus_allowed_ptr(shutdown_task, shuffle_tmp_mask);
+#ifdef CONFIG_HOTPLUG_CPU
+	if (onoff_task)
+		set_cpus_allowed_ptr(onoff_task, shuffle_tmp_mask);

kernel/rcutorture.c static void rcu_torture_shuffle_tasks(void) · line 1349

Quoted 10 lines

kernel/rcutorture.c +10 -0

+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+	if (stall_task)
+		set_cpus_allowed_ptr(stall_task, shuffle_tmp_mask);
+	if (barrier_cbs_tasks)
+		for (i = 0; i < n_barrier_cbs; i++)
+			if (barrier_cbs_tasks[i])
+				set_cpus_allowed_ptr(barrier_cbs_tasks[i],
+						     shuffle_tmp_mask);
+	if (barrier_task)
+		set_cpus_allowed_ptr(barrier_task, shuffle_tmp_mask);

The rest of this seems fine.

- Josh Triplett

Paul E. McKenney

author

2013-01-29 06:41 UTC #6 lore raw

Re: [PATCH tip/core/rcu 4/4] rcu: Make rcutorture's shuffler task shuffle recently added tasks

Quoted 16 lines · Josh Triplett

Quoted 7 lines · Paul E. McKenney
From: "Paul E. McKenney" <[email protected]>
A number of kthreads have been added to rcutorture, but the shuffler task was not informed of them, and thus did not shuffle them. This commit therefore adds the requisite shuffling.
Signed-off-by Paul E. McKenney <[email protected]>
This also makes an unrelated semantic change, and several unrelated whitespace changes.
Quoted 4 lines
---
 kernel/rcutorture.c |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

Quoted 14 lines

kernel/rcutorture.c static int rcu_torture_boost(void *arg) · line 849
Quoted 10 lines
kernel/rcutorture.c +1 -1
index a583f1c..3ebc8bf 100644
@@ -846,7 +846,7 @@ static int rcu_torture_boost(void *arg)
 		/* Wait for the next test interval. */
 		oldstarttime = boost_starttime;
 		while (ULONG_CMP_LT(jiffies, oldstarttime)) {
-			schedule_timeout_uninterruptible(1);
+			schedule_timeout_interruptible(oldstarttime - jiffies);
This change doesn't seem related, and the commit message doesn't explain it either. Could you split it out into a separate commit and document the rationale, please?

Ah, it is related because the shuffling is trying to keep CPUs idle, which means that we don't want all the boost kthreads waking up every CPU every jiffy. I agree that this is not obvious, so I have updated the commit message to call this out.

Quoted 12 lines

kernel/rcutorture.c +0 -1

 			rcu_stutter_wait("rcu_torture_boost");
 			if (kthread_should_stop() ||
 			    fullstop != FULLSTOP_DONTSTOP)

@@ -1318,19 +1318,35 @@ static void rcu_torture_shuffle_tasks(void)
 				set_cpus_allowed_ptr(reader_tasks[i],
 						     shuffle_tmp_mask);
 	}
-
 	if (fakewriter_tasks) {
 		for (i = 0; i < nfakewriters; i++)
 			if (fakewriter_tasks[i])
 				set_cpus_allowed_ptr(fakewriter_tasks[i],

Quoted 8 lines

kernel/rcutorture.c static void rcu_torture_shuffle_tasks(void) · line 1331
Quoted 6 lines
kernel/rcutorture.c +0 -2
 						     shuffle_tmp_mask);
 	}
-
 	if (writer_task)
 		set_cpus_allowed_ptr(writer_task, shuffle_tmp_mask);
-
These three whitespace changes seem unrelated as well.

Some cleanup while in the neighborhood. ;-)

I added this to the commit message as well.

Thanx, Paul

Quoted 26 lines

Quoted 11 lines

kernel/rcutorture.c +9 -0

 	if (stats_task)
 		set_cpus_allowed_ptr(stats_task, shuffle_tmp_mask);
+	if (stutter_task)
+		set_cpus_allowed_ptr(stutter_task, shuffle_tmp_mask);
+	if (fqs_task)
+		set_cpus_allowed_ptr(fqs_task, shuffle_tmp_mask);
+	if (shutdown_task)
+		set_cpus_allowed_ptr(shutdown_task, shuffle_tmp_mask);
+#ifdef CONFIG_HOTPLUG_CPU
+	if (onoff_task)
+		set_cpus_allowed_ptr(onoff_task, shuffle_tmp_mask);

kernel/rcutorture.c static void rcu_torture_shuffle_tasks(void) · line 1349

Quoted 10 lines

kernel/rcutorture.c +10 -0

+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+	if (stall_task)
+		set_cpus_allowed_ptr(stall_task, shuffle_tmp_mask);
+	if (barrier_cbs_tasks)
+		for (i = 0; i < n_barrier_cbs; i++)
+			if (barrier_cbs_tasks[i])
+				set_cpus_allowed_ptr(barrier_cbs_tasks[i],
+						     shuffle_tmp_mask);
+	if (barrier_task)
+		set_cpus_allowed_ptr(barrier_task, shuffle_tmp_mask);

The rest of this seems fine.

- Josh Triplett