On Thu, Apr 10, 2025 at 11:29:03AM -0700, Paul E. McKenney wrote:
> On Thu, Apr 10, 2025 at 11:03:27AM -0400, Joel Fernandes wrote: >
> Currently, the ->gpwrap is not tested (at all per my testing) due to
> the > requirement of a large delta between a CPU's rdp->gp_seq and its
> node's > rnp->gpseq. > > This results in no testing of ->gpwrap being
> set. This patch by default > adds 5 minutes of testing with ->gpwrap
> forced by lowering the delta > between rdp->gp_seq and rnp->gp_seq to
> just 8 GPs. All of this is > configurable, including the active time for
> the setting and a full > testing cycle. > > By default, the first 25
> minutes of a test will have the _default_ > behavior there is right now
> (ULONG_MAX / 4) delta. Then for 5 minutes, > we switch to a smaller delta
> causing 1-2 wraps in 5 minutes. I believe > this is reasonable since we
> at least add a little bit of testing for > usecases where ->gpwrap is set.
> > > Signed-off-by: Joel Fernandes <joelagn...@nvidia.com>
>
> Much better, thank you!
>
> One potential nit below. I will run some tests on this version.
And please feel free to apply the following to both:
Tested-by: Paul E. McKenney <paul...@kernel.org>
> > ---
> > kernel/rcu/rcu.h | 4 +++
> > kernel/rcu/rcutorture.c | 67 ++++++++++++++++++++++++++++++++++++++++-
> > kernel/rcu/tree.c | 34 +++++++++++++++++++--
> > kernel/rcu/tree.h | 1 +
> > 4 files changed, 103 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> > index eed2951a4962..516b26024a37 100644
> > --- a/kernel/rcu/rcu.h
> > +++ b/kernel/rcu/rcu.h
> > @@ -572,6 +572,8 @@ void do_trace_rcu_torture_read(const char
> > *rcutorturename,
> > unsigned long c_old,
> > unsigned long c);
> > void rcu_gp_set_torture_wait(int duration);
> > +void rcu_set_gpwrap_lag(unsigned long lag);
> > +int rcu_get_gpwrap_count(int cpu);
> > #else
> > static inline void rcutorture_get_gp_data(int *flags, unsigned long
> > *gp_seq)
> > {
> > @@ -589,6 +591,8 @@ void do_trace_rcu_torture_read(const char
> > *rcutorturename,
> > do { } while (0)
> > #endif
> > static inline void rcu_gp_set_torture_wait(int duration) { }
> > +static inline void rcu_set_gpwrap_lag(unsigned long lag) { }
> > +static inline int rcu_get_gpwrap_count(int cpu) { return 0; }
> > #endif
> > unsigned long long rcutorture_gather_gp_seqs(void);
> > void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t
> > len);
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index 4fa7772be183..74de92c3a9ab 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -115,6 +115,9 @@ torture_param(int, nreaders, -1, "Number of RCU reader
> > threads");
> > torture_param(int, object_debug, 0, "Enable debug-object double call_rcu()
> > testing");
> > torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs
> > (s)");
> > torture_param(int, onoff_interval, 0, "Time between CPU hotplugs
> > (jiffies), 0=disable");
> > +torture_param(int, gpwrap_lag_cycle_mins, 30, "Total cycle duration for
> > ovf lag testing (in minutes)");
> > +torture_param(int, gpwrap_lag_active_mins, 5, "Duration for which ovf lag
> > is active within each cycle (in minutes)");
> > +torture_param(int, gpwrap_lag_gps, 8, "Value to set for set_gpwrap_lag
> > during an active testing period.");
> > torture_param(int, nocbs_nthreads, 0, "Number of NOCB toggle threads, 0 to
> > disable");
> > torture_param(int, nocbs_toggle, 1000, "Time between toggling nocb state
> > (ms)");
> > torture_param(int, preempt_duration, 0, "Preemption duration (ms), zero to
> > disable");
> > @@ -413,6 +416,8 @@ struct rcu_torture_ops {
> > bool (*reader_blocked)(void);
> > unsigned long long (*gather_gp_seqs)(void);
> > void (*format_gp_seqs)(unsigned long long seqs, char *cp, size_t len);
> > + void (*set_gpwrap_lag)(unsigned long lag);
> > + int (*get_gpwrap_count)(int cpu);
> > long cbflood_max;
> > int irq_capable;
> > int can_boost;
> > @@ -619,6 +624,8 @@ static struct rcu_torture_ops rcu_ops = {
> > : NULL,
> > .gather_gp_seqs = rcutorture_gather_gp_seqs,
> > .format_gp_seqs = rcutorture_format_gp_seqs,
> > + .set_gpwrap_lag = rcu_set_gpwrap_lag,
> > + .get_gpwrap_count = rcu_get_gpwrap_count,
> > .irq_capable = 1,
> > .can_boost = IS_ENABLED(CONFIG_RCU_BOOST),
> > .extendables = RCUTORTURE_MAX_EXTEND,
> > @@ -2394,6 +2401,7 @@ rcu_torture_stats_print(void)
> > int i;
> > long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> > long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> > + long n_gpwraps = 0;
> > struct rcu_torture *rtcp;
> > static unsigned long rtcv_snap = ULONG_MAX;
> > static bool splatted;
> > @@ -2404,6 +2412,7 @@ rcu_torture_stats_print(void)
> > pipesummary[i] += READ_ONCE(per_cpu(rcu_torture_count,
> > cpu)[i]);
> > batchsummary[i] += READ_ONCE(per_cpu(rcu_torture_batch,
> > cpu)[i]);
> > }
> > + n_gpwraps += cur_ops->get_gpwrap_count(cpu);
> > }
> > for (i = RCU_TORTURE_PIPE_LEN; i >= 0; i--) {
> > if (pipesummary[i] != 0)
> > @@ -2435,8 +2444,9 @@ rcu_torture_stats_print(void)
> > data_race(n_barrier_attempts),
> > data_race(n_rcu_torture_barrier_error));
> > pr_cont("read-exits: %ld ", data_race(n_read_exits)); // Statistic.
> > - pr_cont("nocb-toggles: %ld:%ld\n",
> > + pr_cont("nocb-toggles: %ld:%ld ",
> > atomic_long_read(&n_nocb_offload),
> > atomic_long_read(&n_nocb_deoffload));
> > + pr_cont("gpwraps: %ld\n", n_gpwraps);
> >
> > pr_alert("%s%s ", torture_type, TORTURE_FLAG);
> > if (atomic_read(&n_rcu_torture_mberror) ||
> > @@ -3607,6 +3617,54 @@ static int rcu_torture_preempt(void *unused)
> >
> > static enum cpuhp_state rcutor_hp;
> >
> > +static struct hrtimer gpwrap_lag_timer;
> > +static bool gpwrap_lag_active;
> > +
> > +/* Timer handler for toggling RCU grace-period sequence overflow test lag
> > value */
> > +static enum hrtimer_restart rcu_gpwrap_lag_timer(struct hrtimer *timer)
> > +{
> > + ktime_t next_delay;
> > +
> > + if (gpwrap_lag_active) {
> > + pr_alert("rcu-torture: Disabling ovf lag (value=0)\n");
> > + cur_ops->set_gpwrap_lag(0);
> > + gpwrap_lag_active = false;
> > + next_delay = ktime_set((gpwrap_lag_cycle_mins -
> > gpwrap_lag_active_mins) * 60, 0);
> > + } else {
> > + pr_alert("rcu-torture: Enabling ovf lag (value=%d)\n",
> > gpwrap_lag_gps);
> > + cur_ops->set_gpwrap_lag(gpwrap_lag_gps);
> > + gpwrap_lag_active = true;
> > + next_delay = ktime_set(gpwrap_lag_active_mins * 60, 0);
> > + }
> > +
> > + if (torture_must_stop())
> > + return HRTIMER_NORESTART;
> > +
> > + hrtimer_forward_now(timer, next_delay);
> > + return HRTIMER_RESTART;
> > +}
> > +
> > +static int rcu_gpwrap_lag_init(void)
> > +{
> > + if (gpwrap_lag_cycle_mins <= 0 || gpwrap_lag_active_mins <= 0) {
> > + pr_alert("rcu-torture: lag timing parameters must be
> > positive\n");
> > + return -EINVAL;
>
> When rcutorture is initiated by modprobe, this makes perfect sense.
>
> But if rcutorture is built in, we have other choices: (1) Disable gpwrap
> testing and do other testing but splat so that the bogus scripting can
> be fixed, (2) Force default values and splat as before, (3) Splat and
> halt the system.
>
> The usual approach has been #1, but what makes sense in this case?
>
> > + }
> > +
> > + hrtimer_setup(&gpwrap_lag_timer, rcu_gpwrap_lag_timer, CLOCK_MONOTONIC,
> > HRTIMER_MODE_REL);
> > + gpwrap_lag_active = false;
> > + hrtimer_start(&gpwrap_lag_timer,
> > + ktime_set((gpwrap_lag_cycle_mins -
> > gpwrap_lag_active_mins) * 60, 0), HRTIMER_MODE_REL);
> > +
> > + return 0;
> > +}
> > +
> > +static void rcu_gpwrap_lag_cleanup(void)
> > +{
> > + hrtimer_cancel(&gpwrap_lag_timer);
> > + cur_ops->set_gpwrap_lag(0);
> > + gpwrap_lag_active = false;
> > +}
> > static void
> > rcu_torture_cleanup(void)
> > {
> > @@ -3776,6 +3834,9 @@ rcu_torture_cleanup(void)
> > torture_cleanup_end();
> > if (cur_ops->gp_slow_unregister)
> > cur_ops->gp_slow_unregister(NULL);
> > +
> > + if (cur_ops->set_gpwrap_lag)
> > + rcu_gpwrap_lag_cleanup();
> > }
> >
> > static void rcu_torture_leak_cb(struct rcu_head *rhp)
> > @@ -4275,6 +4336,10 @@ rcu_torture_init(void)
> > torture_init_end();
> > if (cur_ops->gp_slow_register &&
> > !WARN_ON_ONCE(!cur_ops->gp_slow_unregister))
> > cur_ops->gp_slow_register(&rcu_fwd_cb_nodelay);
> > +
> > + if (cur_ops->set_gpwrap_lag && rcu_gpwrap_lag_init())
> > + goto unwind;
> > +
> > return 0;
> >
> > unwind:
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 659f83e71048..6ec30d07759d 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -80,6 +80,15 @@ static void rcu_sr_normal_gp_cleanup_work(struct
> > work_struct *);
> > static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
> > .gpwrap = true,
> > };
> > +
> > +int rcu_get_gpwrap_count(int cpu)
> > +{
> > + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> > +
> > + return READ_ONCE(rdp->gpwrap_count);
> > +}
> > +EXPORT_SYMBOL_GPL(rcu_get_gpwrap_count);
> > +
> > static struct rcu_state rcu_state = {
> > .level = { &rcu_state.node[0] },
> > .gp_state = RCU_GP_IDLE,
> > @@ -757,6 +766,25 @@ void rcu_request_urgent_qs_task(struct task_struct *t)
> > smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
> > }
> >
> > +/**
> > + * rcu_set_gpwrap_lag - Set RCU GP sequence overflow lag value.
> > + * @lag_gps: Set overflow lag to this many grace period worth of counters
> > + * which is used by rcutorture to quickly force a gpwrap situation.
> > + * @lag_gps = 0 means we reset it back to the boot-time value.
> > + */
> > +static unsigned long seq_gpwrap_lag = ULONG_MAX / 4;
> > +
> > +void rcu_set_gpwrap_lag(unsigned long lag_gps)
> > +{
> > + unsigned long lag_seq_count;
> > +
> > + lag_seq_count = (lag_gps == 0)
> > + ? ULONG_MAX / 4
> > + : lag_gps << RCU_SEQ_CTR_SHIFT;
> > + WRITE_ONCE(seq_gpwrap_lag, lag_seq_count);
> > +}
> > +EXPORT_SYMBOL_GPL(rcu_set_gpwrap_lag);
> > +
> > /*
> > * When trying to report a quiescent state on behalf of some other CPU,
> > * it is our responsibility to check for and handle potential overflow
> > @@ -767,9 +795,11 @@ void rcu_request_urgent_qs_task(struct task_struct *t)
> > static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
> > {
> > raw_lockdep_assert_held_rcu_node(rnp);
> > - if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
> > - rnp->gp_seq))
> > + if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + seq_gpwrap_lag,
> > + rnp->gp_seq)) {
> > WRITE_ONCE(rdp->gpwrap, true);
> > + WRITE_ONCE(rdp->gpwrap_count, READ_ONCE(rdp->gpwrap_count) + 1);
> > + }
> > if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
> > rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
> > }
> > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> > index a9a811d9d7a3..63bea388c243 100644
> > --- a/kernel/rcu/tree.h
> > +++ b/kernel/rcu/tree.h
> > @@ -183,6 +183,7 @@ struct rcu_data {
> > bool core_needs_qs; /* Core waits for quiescent state. */
> > bool beenonline; /* CPU online at least once. */
> > bool gpwrap; /* Possible ->gp_seq wrap. */
> > + unsigned int gpwrap_count; /* Count of GP sequence wrap. */
> > bool cpu_started; /* RCU watching this onlining CPU. */
> > struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
> > unsigned long grpmask; /* Mask to apply to leaf qsmask. */
> > --
> > 2.43.0
> >
