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rcutorture: Fully test lazy RCU

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Currently, rcutorture bypasses lazy RCU by using call_rcu_hurry().
This works, avoiding the dreaded rtort_pipe_count WARN(), but fails to
fully test lazy RCU.  The rtort_pipe_count WARN() splats because lazy RCU
could delay the start of an RCU grace period for a full stutter period,
which defaults to only three seconds.

This commit therefore reverts the call_rcu_hurry() instances
back to call_rcu(), but, in kernels built with CONFIG_RCU_LAZY=y,
queues a workqueue handler just before the call to stutter_wait() in
rcu_torture_writer().  This workqueue handler invokes rcu_barrier(),
which motivates any lingering lazy callbacks, thus avoiding the splat.

Reported-by: Saravana Kannan <saravanak@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
This commit is contained in:
Paul E. McKenney
2026-05-07 09:57:15 -07:00
committed by Uladzislau Rezki (Sony)
parent 5200f5f493
commit aa61e8b4fb
1 changed files with 26 additions and 3 deletions
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29
kernel/rcu/rcutorture.c
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@@ -572,7 +572,7 @@ static unsigned long rcu_no_completed(void)
static void rcu_torture_deferred_free(struct rcu_torture *p)
{
call_rcu_hurry(&p->rtort_rcu, rcu_torture_cb);
call_rcu(&p->rtort_rcu, rcu_torture_cb);
}
static void rcu_sync_torture_init(void)
@@ -619,7 +619,7 @@ static struct rcu_torture_ops rcu_ops = {
.poll_gp_state_exp = poll_state_synchronize_rcu,
.cond_sync_exp = cond_synchronize_rcu_expedited,
.cond_sync_exp_full = cond_synchronize_rcu_expedited_full,
.call = call_rcu_hurry,
.call = call_rcu,
.cb_barrier = rcu_barrier,
.fqs = rcu_force_quiescent_state,
.gp_kthread_dbg = show_rcu_gp_kthreads,
@@ -1145,7 +1145,7 @@ static void rcu_tasks_torture_deferred_free(struct rcu_torture *p)
static void synchronize_rcu_mult_test(void)
{
synchronize_rcu_mult(call_rcu_tasks, call_rcu_hurry);
synchronize_rcu_mult(call_rcu_tasks, call_rcu);
}
static struct rcu_torture_ops tasks_ops = {
@@ -1631,6 +1631,17 @@ static void do_rtws_sync(struct torture_random_state *trsp, void (*sync)(void))
cpus_read_unlock();
}
/*
* Do an rcu_barrier() to motivate lazy callbacks during a stutter
* pause. Without this, we can get false-positives rtort_pipe_count
* splats.
*/
static void rcu_torture_writer_work(struct work_struct *work)
{
if (cur_ops->cb_barrier)
cur_ops->cb_barrier();
}
/*
* RCU torture writer kthread. Repeatedly substitutes a new structure
* for that pointed to by rcu_torture_current, freeing the old structure
@@ -1651,6 +1662,7 @@ rcu_torture_writer(void *arg)
int i;
int idx;
unsigned long j;
struct work_struct lazy_work;
int oldnice = task_nice(current);
struct rcu_gp_oldstate *rgo = NULL;
int rgo_size = 0;
@@ -1703,6 +1715,9 @@ rcu_torture_writer(void *arg)
pr_alert("%s" TORTURE_FLAG " Waited %lu jiffies for boot to complete.\n",
torture_type, jiffies - j);
if (IS_ENABLED(CONFIG_RCU_LAZY))
INIT_WORK_ONSTACK(&lazy_work, rcu_torture_writer_work);
do {
rcu_torture_writer_state = RTWS_FIXED_DELAY;
torture_hrtimeout_us(500, 1000, &rand);
@@ -1895,6 +1910,8 @@ rcu_torture_writer(void *arg)
!rcu_gp_is_normal();
}
rcu_torture_writer_state = RTWS_STUTTER;
if (IS_ENABLED(CONFIG_RCU_LAZY))
queue_work(system_percpu_wq, &lazy_work);
stutter_waited = stutter_wait("rcu_torture_writer");
if (stutter_waited &&
!atomic_read(&rcu_fwd_cb_nodelay) &&
@@ -1925,6 +1942,12 @@ rcu_torture_writer(void *arg)
pr_alert("%s" TORTURE_FLAG
" Dynamic grace-period expediting was disabled.\n",
torture_type);
if (IS_ENABLED(CONFIG_RCU_LAZY)) {
cancel_work_sync(&lazy_work);
destroy_work_on_stack(&lazy_work);
}
kfree(ulo);
kfree(rgo);
rcu_torture_writer_state = RTWS_STOPPING;