* [PATCH v4 1/2] rcutorture: Perform more frequent testing of ->gpwrap
2025-04-15 13:36 [PATCH v4 0/2] My new rcutorture patches for 6.15 Joel Fernandes
@ 2025-04-15 13:36 ` Joel Fernandes
2025-04-15 13:36 ` [PATCH v4 2/2] rcutorture: Fix issue with re-using old images on ARM64 Joel Fernandes
2025-04-15 13:40 ` [PATCH v4 0/2] My new rcutorture patches for 6.15 Joel Fernandes
2 siblings, 0 replies; 5+ messages in thread
From: Joel Fernandes @ 2025-04-15 13:36 UTC (permalink / raw)
To: linux-kernel, Paul E. McKenney, Frederic Weisbecker,
Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Boqun Feng,
Uladzislau Rezki, Steven Rostedt, Mathieu Desnoyers,
Lai Jiangshan, Zqiang, Davidlohr Bueso
Cc: Joel Fernandes, rcu
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.
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
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;
+ }
+
+ 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
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