>
> From: "Paul E. McKenney" <[email protected]>
>
> 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.
>
> Questions for review:
>
> 1. Should we avoid queueing work for RCU implementations not
> supporting lazy callbacks?
Hello, Paul
maybe we can do this:
rcu_ops = {
...
.support_lazy = IS_ENABLED(CONFIG_RCU_LAZY),
};
and
if (cur_ops->support_lazy )
queue_work(..., &lazy_work);
>
> 2. Should we avoid queueing work in kernels built with
> CONFIG_RCU_LAZY=y, but that were not booted with the
> rcutree.enable_rcu_lazy kernel boot parameter set? (Note that
> this requires some ugliness to access this parameter, and must
> also handle Tiny RCU.)
>
> 3. Does the rcu_torture_ops structure need a ->call_hurry() field,
> and if so, why? If not, why not?
>
> 4. Your additional questions here!
>
> Reported-by: Saravana Kannan <[email protected]>
> Signed-off-by: Paul E. McKenney <[email protected]>
> Signed-off-by: Uladzislau Rezki (Sony) <[email protected]>
> ---
> kernel/rcu/rcutorture.c | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 5f2848b828dc..91ba3160ba6a 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -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;
> @@ -1667,6 +1679,7 @@ rcu_torture_writer(void *arg)
> stallsdone += (stall_cpu_holdoff + stall_gp_kthread +
> stall_cpu + 60) *
> HZ * (stall_cpu_repeat + 1);
> VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
> + INIT_WORK_ONSTACK(&lazy_work, rcu_torture_writer_work);
> if (!can_expedite)
> pr_alert("%s" TORTURE_FLAG
> " GP expediting controlled from boot/sysfs for
> %s.\n",
> @@ -1895,6 +1908,8 @@ 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);
When the task ends, the lazy_work should be cancel and destroy:
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f593f8b794dd..5adf537ab410 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1682,7 +1682,6 @@ rcu_torture_writer(void *arg)
stallsdone += (stall_cpu_holdoff + stall_gp_kthread + stall_cpu + 60) *
HZ * (stall_cpu_repeat + 1);
VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
- INIT_WORK_ONSTACK(&lazy_work, rcu_torture_writer_work);
if (!can_expedite)
pr_alert("%s" TORTURE_FLAG
" GP expediting controlled from boot/sysfs for %s.\n",
@@ -1719,6 +1718,8 @@ rcu_torture_writer(void *arg)
pr_alert("%s" TORTURE_FLAG " Waited %lu jiffies for boot to complete.\n",
torture_type, jiffies - j);
+ INIT_WORK_ONSTACK(&lazy_work, rcu_torture_writer_work);
+
do {
rcu_torture_writer_state = RTWS_FIXED_DELAY;
torture_hrtimeout_us(500, 1000, &rand);
@@ -1943,6 +1944,9 @@ 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;
Thanks
Zqiang
> stutter_waited = stutter_wait("rcu_torture_writer");
> if (stutter_waited &&
> !atomic_read(&rcu_fwd_cb_nodelay) &&
> --
> 2.47.3
>
>
