Commit c682db55 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcutorture: Add trivial RCU implementation 



I have been showing off a trivial RCU implementation for non-preemptive
environments for some time now:

	#define rcu_read_lock()
	#define rcu_read_unlock()
	#define rcu_dereference(p) READ_ONCE(p)
	#define rcu_assign_pointer(p, v) smp_store_release(&(p), (v))
	void synchronize_rcu(void)
	{
	int cpu;
		for_each_online_cpu(cpu)
			sched_setaffinity(current->pid, cpumask_of(cpu));
	}

Trivial or not, as the old saying goes, "if it ain't tested, it don't
work!".  This commit therefore adds a "trivial" flavor to rcutorture
and a corresponding TRIVIAL test scenario.  This variant does not handle
CPU hotplug, which is unconditionally enabled on x86 for post-v5.1-rc3
kernels, which is why the TRIVIAL.boot says "rcutorture.onoff_interval=0".
This commit actually does handle CONFIG_PREEMPT=y kernels, but only
because it turns back the Linux-kernel clock in order to provide these
alternative definitions (or the moral equivalent thereof):

	#define rcu_read_lock() preempt_disable()
	#define rcu_read_unlock() preempt_enable()

In CONFIG_PREEMPT=n kernels without debugging, these are equivalent to
empty macros give or take a compiler barrier.  However, the have been
successfully tested with actual empty macros as well.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Fix symbol issue reported by kbuild test robot <lkp@intel.com>. ]
[ paulmck: Work around sched_setaffinity() issue noted by Andrea Parri. ]
[ paulmck: Add rcutorture.shuffle_interval=0 to TRIVIAL.boot to fix
  interaction with shuffler task noted by Peter Zijlstra. ]
Tested-by: default avatarAndrea Parri <andrea.parri@amarulasolutions.com>
parent 3432d765

kernel/rcu/rcu.h

+5 −0
Original line number Diff line number Diff line
@@ -446,6 +446,7 @@ void rcu_request_urgent_qs_task(struct task_struct *t); 
enum rcutorture_type {

	RCU_FLAVOR,

	RCU_TASKS_FLAVOR,

	RCU_TRIVIAL_FLAVOR,

	SRCU_FLAVOR,

	INVALID_RCU_FLAVOR

};
@@ -479,6 +480,10 @@ void do_trace_rcu_torture_read(const char *rcutorturename, 
#endif

#endif



#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)

long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask);

#endif



#ifdef CONFIG_TINY_SRCU



static inline void srcutorture_get_gp_data(enum rcutorture_type test_type,

kernel/rcu/rcutorture.c

+44 −1
Original line number Diff line number Diff line
@@ -672,6 +672,47 @@ static struct rcu_torture_ops tasks_ops = { 
	.name		= "tasks"

};



/*

 * Definitions for trivial CONFIG_PREEMPT=n-only torture testing.

 * This implementation does not necessarily work well with CPU hotplug.

 */



static void synchronize_rcu_trivial(void)

{

	int cpu;



	for_each_online_cpu(cpu) {

		rcutorture_sched_setaffinity(current->pid, cpumask_of(cpu));

		WARN_ON_ONCE(raw_smp_processor_id() != cpu);

	}

}



static int rcu_torture_read_lock_trivial(void) __acquires(RCU)

{

	preempt_disable();

	return 0;

}



static void rcu_torture_read_unlock_trivial(int idx) __releases(RCU)

{

	preempt_enable();

}



static struct rcu_torture_ops trivial_ops = {

	.ttype		= RCU_TRIVIAL_FLAVOR,

	.init		= rcu_sync_torture_init,

	.readlock	= rcu_torture_read_lock_trivial,

	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */

	.readunlock	= rcu_torture_read_unlock_trivial,

	.get_gp_seq	= rcu_no_completed,

	.sync		= synchronize_rcu_trivial,

	.exp_sync	= synchronize_rcu_trivial,

	.fqs		= NULL,

	.stats		= NULL,

	.irq_capable	= 1,

	.name		= "trivial"

};



static unsigned long rcutorture_seq_diff(unsigned long new, unsigned long old)

{

	if (!cur_ops->gp_diff)
@@ -1789,6 +1830,8 @@ static void rcu_torture_fwd_prog_cr(void) 


	if (READ_ONCE(rcu_fwd_emergency_stop))

		return; /* Get out of the way quickly, no GP wait! */

	if (!cur_ops->call)

		return; /* Can't do call_rcu() fwd prog without ->call. */



	/* Loop continuously posting RCU callbacks. */

	WRITE_ONCE(rcu_fwd_cb_nodelay, true);
@@ -2265,7 +2308,7 @@ rcu_torture_init(void) 
	int firsterr = 0;

	static struct rcu_torture_ops *torture_ops[] = {

		&rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,

		&busted_srcud_ops, &tasks_ops,

		&busted_srcud_ops, &tasks_ops, &trivial_ops,

	};



	if (!torture_init_begin(torture_type, verbose))

kernel/rcu/update.c

+13 −0
Original line number Diff line number Diff line
@@ -423,6 +423,19 @@ EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); 
	do { } while (0)

#endif



#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)

/* Get rcutorture access to sched_setaffinity(). */

long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)

{

	int ret;



	ret = sched_setaffinity(pid, in_mask);

	WARN_ONCE(ret, "%s: sched_setaffinity() returned %d\n", __func__, ret);

	return ret;

}

EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity);

#endif



#ifdef CONFIG_RCU_STALL_COMMON

int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */

EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);

tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL

0 → 100644
+14 −0
Original line number Diff line number Diff line 
CONFIG_SMP=y

CONFIG_NR_CPUS=8

CONFIG_PREEMPT_NONE=y

CONFIG_PREEMPT_VOLUNTARY=n

CONFIG_PREEMPT=n

CONFIG_HZ_PERIODIC=n

CONFIG_NO_HZ_IDLE=y

CONFIG_NO_HZ_FULL=n

CONFIG_HOTPLUG_CPU=n

CONFIG_SUSPEND=n

CONFIG_HIBERNATION=n

CONFIG_DEBUG_LOCK_ALLOC=n

CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TRIVIAL.boot

0 → 100644
+3 −0
Original line number Diff line number Diff line 
rcutorture.torture_type=trivial

rcutorture.onoff_interval=0

rcutorture.shuffle_interval=0

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