Commit 1b27291b authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcutorture: Add forward-progress tests for RCU grace periods 



This commit adds a kthread that loops going into and out of RCU
read-side critical sections, but also including a cond_resched(),
optionally guarded by a check of need_resched(), in that same loop.
This commit relies solely on rcu_torture_writer() progress to judge
the forward progress of grace periods.

Note that Tasks RCU and SRCU are exempted from forward-progress testing
due their (intentionally) less-robust forward-progress guarantees.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent a52d14ad

include/linux/rcutiny.h

+1 −0
Original line number Diff line number Diff line
@@ -108,6 +108,7 @@ static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt) 
 */

static inline void rcu_virt_note_context_switch(int cpu) { }

static inline void rcu_cpu_stall_reset(void) { }

static inline int rcu_jiffies_till_stall_check(void) { return 21 * HZ; }

static inline void rcu_idle_enter(void) { }

static inline void rcu_idle_exit(void) { }

static inline void rcu_irq_enter(void) { }

kernel/rcu/rcutorture.c

+72 −1
Original line number Diff line number Diff line
@@ -89,6 +89,12 @@ torture_param(int, fqs_duration, 0, 
	      "Duration of fqs bursts (us), 0 to disable");

torture_param(int, fqs_holdoff, 0, "Holdoff time within fqs bursts (us)");

torture_param(int, fqs_stutter, 3, "Wait time between fqs bursts (s)");

torture_param(bool, fwd_progress, 1, "Test grace-period forward progress");

torture_param(int, fwd_progress_div, 4, "Fraction of CPU stall to wait");

torture_param(int, fwd_progress_holdoff, 60,

	      "Time between forward-progress tests (s)");

torture_param(bool, fwd_progress_need_resched, 1,

	      "Hide cond_resched() behind need_resched()");

torture_param(bool, gp_cond, false, "Use conditional/async GP wait primitives");

torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");

torture_param(bool, gp_normal, false,
@@ -137,6 +143,7 @@ static struct task_struct **cbflood_task; 
static struct task_struct *fqs_task;

static struct task_struct *boost_tasks[NR_CPUS];

static struct task_struct *stall_task;

static struct task_struct *fwd_prog_task;

static struct task_struct **barrier_cbs_tasks;

static struct task_struct *barrier_task;
@@ -291,6 +298,7 @@ struct rcu_torture_ops { 
	void (*cb_barrier)(void);

	void (*fqs)(void);

	void (*stats)(void);

	int (*stall_dur)(void);

	int irq_capable;

	int can_boost;

	int extendables;
@@ -429,6 +437,7 @@ static struct rcu_torture_ops rcu_ops = { 
	.cb_barrier	= rcu_barrier,

	.fqs		= rcu_force_quiescent_state,

	.stats		= NULL,

	.stall_dur	= rcu_jiffies_till_stall_check,

	.irq_capable	= 1,

	.can_boost	= rcu_can_boost(),

	.name		= "rcu"
@@ -1116,7 +1125,8 @@ rcu_torture_writer(void *arg) 
				break;

			}

		}

		rcu_torture_current_version++;

		WRITE_ONCE(rcu_torture_current_version,

			   rcu_torture_current_version + 1);

		/* Cycle through nesting levels of rcu_expedite_gp() calls. */

		if (can_expedite &&

		    !(torture_random(&rand) & 0xff & (!!expediting - 1))) {
@@ -1660,6 +1670,63 @@ static int __init rcu_torture_stall_init(void) 
	return torture_create_kthread(rcu_torture_stall, NULL, stall_task);

}



/* Carry out grace-period forward-progress testing. */

static int rcu_torture_fwd_prog(void *args)

{

	unsigned long cvar;

	int idx;

	unsigned long stopat;

	bool tested = false;



	VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");

	do {

		schedule_timeout_interruptible(fwd_progress_holdoff * HZ);

		cvar = READ_ONCE(rcu_torture_current_version);

		stopat = jiffies + cur_ops->stall_dur() / fwd_progress_div;

		while (time_before(jiffies, stopat) && !torture_must_stop()) {

			idx = cur_ops->readlock();

			udelay(10);

			cur_ops->readunlock(idx);

			if (!fwd_progress_need_resched || need_resched())

				cond_resched();

		}

		if (!time_before(jiffies, stopat) && !torture_must_stop()) {

			tested = true;

			WARN_ON_ONCE(cvar ==

				     READ_ONCE(rcu_torture_current_version));

		}

		/* Avoid slow periods, better to test when busy. */

		stutter_wait("rcu_torture_fwd_prog");

	} while (!torture_must_stop());

	WARN_ON(!tested);

	torture_kthread_stopping("rcu_torture_fwd_prog");

	return 0;

}



/* If forward-progress checking is requested and feasible, spawn the thread. */

static int __init rcu_torture_fwd_prog_init(void)

{

	if (!fwd_progress)

		return 0; /* Not requested, so don't do it. */

	if (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0) {

		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");

		return 0;

	}

	if (stall_cpu > 0) {

		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, conflicts with CPU-stall testing");

		if (IS_MODULE(CONFIG_RCU_TORTURE_TESTS))

			return -EINVAL; /* In module, can fail back to user. */

		WARN_ON(1); /* Make sure rcutorture notices conflict. */

		return 0;

	}

	if (fwd_progress_holdoff <= 0)

		fwd_progress_holdoff = 1;

	if (fwd_progress_div <= 0)

		fwd_progress_div = 4;

	return torture_create_kthread(rcu_torture_fwd_prog,

				      NULL, fwd_prog_task);

}



/* Callback function for RCU barrier testing. */

static void rcu_torture_barrier_cbf(struct rcu_head *rcu)

{
@@ -1833,6 +1900,7 @@ rcu_torture_cleanup(void) 
	}



	rcu_torture_barrier_cleanup();

	torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);

	torture_stop_kthread(rcu_torture_stall, stall_task);

	torture_stop_kthread(rcu_torture_writer, writer_task);
@@ -2104,6 +2172,9 @@ rcu_torture_init(void) 
	if (firsterr)

		goto unwind;

	firsterr = rcu_torture_stall_init();

	if (firsterr)

		goto unwind;

	firsterr = rcu_torture_fwd_prog_init();

	if (firsterr)

		goto unwind;

	firsterr = rcu_torture_barrier_init();

kernel/rcu/update.c

+1 −0
Original line number Diff line number Diff line
@@ -472,6 +472,7 @@ int rcu_jiffies_till_stall_check(void) 
	}

	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;

}

EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);



void rcu_sysrq_start(void)

{

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