// SPDX-License-Identifier: GPL-2.0+
/*
* RCU CPU stall warnings for normal RCU grace periods
*
* Copyright IBM Corporation, 2019
*
* Author: Paul E. McKenney <paulmck@linux.ibm.com>
*/
//////////////////////////////////////////////////////////////////////////////
//
// Controlling CPU stall warnings, including delay calculation.
/* panic() on RCU Stall sysctl. */
int sysctl_panic_on_rcu_stall __read_mostly;
#ifdef CONFIG_PROVE_RCU
#define RCU_STALL_DELAY_DELTA (5 * HZ)
#else
#define RCU_STALL_DELAY_DELTA 0
#endif
/* Limit-check stall timeouts specified at boottime and runtime. */
int rcu_jiffies_till_stall_check(void)
{
int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
/*
* Limit check must be consistent with the Kconfig limits
* for CONFIG_RCU_CPU_STALL_TIMEOUT.
*/
if (till_stall_check < 3) {
WRITE_ONCE(rcu_cpu_stall_timeout, 3);
till_stall_check = 3;
} else if (till_stall_check > 300) {
WRITE_ONCE(rcu_cpu_stall_timeout, 300);
till_stall_check = 300;
}
return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}
EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
/* Don't do RCU CPU stall warnings during long sysrq printouts. */
void rcu_sysrq_start(void)
{
if (!rcu_cpu_stall_suppress)
rcu_cpu_stall_suppress = 2;
}
void rcu_sysrq_end(void)
{
if (rcu_cpu_stall_suppress == 2)
rcu_cpu_stall_suppress = 0;
}
/* Don't print RCU CPU stall warnings during a kernel panic. */
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
{
rcu_cpu_stall_suppress = 1;
return NOTIFY_DONE;
}
static struct notifier_block rcu_panic_block = {
.notifier_call = rcu_panic,
};
static int __init check_cpu_stall_init(void)
{
atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
return 0;
}
early_initcall(check_cpu_stall_init);
/* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
static void panic_on_rcu_stall(void)
{
if (sysctl_panic_on_rcu_stall)
panic("RCU Stall\n");
}
/**
* rcu_cpu_stall_reset - prevent further stall warnings in current grace period
*
* Set the stall-warning timeout way off into the future, thus preventing
* any RCU CPU stall-warning messages from appearing in the current set of
* RCU grace periods.
*
* The caller must disable hard irqs.
*/
void rcu_cpu_stall_reset(void)
{
WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
}
//////////////////////////////////////////////////////////////////////////////
//
// Interaction with RCU grace periods
/* Start of new grace period, so record stall time (and forcing times). */
static void record_gp_stall_check_time(void)
{
unsigned long j = jiffies;
unsigned long j1;
rcu_state.gp_start = j;
j1 = rcu_jiffies_till_stall_check();
/* Record ->gp_start before ->jiffies_stall. */
smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
rcu_state.jiffies_resched = j + j1 / 2;
rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
}
/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
rdp->ticks_this_gp = 0;
rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}
/*
* If too much time has passed in the current grace period, and if
* so configured, go kick the relevant kthreads.
*/
static void rcu_stall_kick_kthreads(void)
{
unsigned long j;
if (!rcu_kick_kthreads)
return;
j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
if (time_after(jiffies, j) && rcu_state.gp_kthread &&
(rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
WARN_ONCE(1, "Kicking %s grace-period kthread\n",
rcu_state.name);
rcu_ftrace_dump(DUMP_ALL);
wake_up_process(rcu_state.gp_kthread);
WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
}
}
/*
* Handler for the irq_work request posted about halfway into the RCU CPU
* stall timeout, and used to detect excessive irq disabling. Set state
* appropriately, but just complain if there is unexpected state on entry.
*/
static void rcu_iw_handler(struct irq_work *iwp)
{
struct rcu_data *rdp;
struct rcu_node *rnp;
rdp = container_of(iwp, struct rcu_data, rcu_iw);
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp);
if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
rdp->rcu_iw_gp_seq = rnp->gp_seq;
rdp->rcu_iw_pending = false;
}
raw_spin_unlock_rcu_node(rnp);
}
//////////////////////////////////////////////////////////////////////////////
//
// Printing RCU CPU stall warnings
#ifdef CONFIG_PREEMPT
/*
* Dump detailed information for all tasks blocking the current RCU
* grace period on the specified rcu_node structure.
*/
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
unsigned long flags;
struct task_struct *t;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (!rcu_preempt_blocked_readers_cgp(rnp)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
t = list_entry(rnp->gp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
/*
* We could be printing a lot while holding a spinlock.
* Avoid triggering hard lockup.
*/
touch_nmi_watchdog();
sched_show_task(t);
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, printing out the tid of each.
*/
static int rcu_print_task_stall(struct rcu_node *rnp)
{
struct task_struct *t;
int ndetected = 0;
if (!rcu_preempt_blocked_readers_cgp(rnp))
return 0;
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
t = list_entry(rnp->gp_tasks->prev,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
pr_cont(" P%d", t->pid);
ndetected++;
}
pr_cont("\n");
return ndetected;
}
#else /* #ifdef CONFIG_PREEMPT */
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
}
/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
static int rcu_print_task_stall(struct rcu_node *rnp)
{
return 0;
}
#endif /* #else #ifdef CONFIG_PREEMPT */
/*
* Dump stacks of all tasks running on stalled CPUs. First try using
* NMIs, but fall back to manual remote stack tracing on architectures
* that don't support NMI-based stack dumps. The NMI-triggered stack
* traces are more accurate because they are printed by the target CPU.
*/
static void rcu_dump_cpu_stacks(void)
{
int cpu;
unsigned long flags;
struct rcu_node *rnp;
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
for_each_leaf_node_possible_cpu(rnp, cpu)
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
if (!trigger_single_cpu_backtrace(cpu))
dump_cpu_task(cpu);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
#ifdef CONFIG_RCU_FAST_NO_HZ
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
rdp->last_accelerate & 0xffff, jiffies & 0xffff,
".l"[rdp->all_lazy],
".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
".D"[!!rdp->tick_nohz_enabled_snap]);
}
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
*cp = '\0';
}
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
/*
* Print out diagnostic information for the specified stalled CPU.
*
* If the specified CPU is aware of the current RCU grace period, then
* print the number of scheduling clock interrupts the CPU has taken
* during the time that it has been aware. Otherwise, print the number
* of RCU grace periods that this CPU is ignorant of, for example, "1"
* if the CPU was aware of the previous grace period.
*
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
*/
static void print_cpu_stall_info(int cpu)
{
unsigned long delta;
char fast_no_hz[72];
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
char *ticks_title;
unsigned long ticks_value;
/*
* We could be printing a lot while holding a spinlock. Avoid
* triggering hard lockup.
*/
touch_nmi_watchdog();
ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
if (ticks_value) {
ticks_title = "GPs behind";
} else {
ticks_title = "ticks this GP";
ticks_value = rdp->ticks_this_gp;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
cpu,
"O."[!!cpu_online(cpu)],
"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
"N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
!IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
"!."[!delta],
ticks_value, ticks_title,
rcu_dynticks_snap(rdp) & 0xfff,
rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
fast_no_hz);
}
/* Complain about starvation of grace-period kthread. */
static void rcu_check_gp_kthread_starvation(void)
{
struct task_struct *gpk = rcu_state.gp_kthread;
unsigned long j;
j = jiffies - READ_ONCE(rcu_state.gp_activity);
if (j > 2 * HZ) {
pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
rcu_state.name, j,
(long)rcu_seq_current(&rcu_state.gp_seq),
READ_ONCE(rcu_state.gp_flags),
gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
if (gpk) {
pr_err("RCU grace-period kthread stack dump:\n");
sched_show_task(gpk);
wake_up_process(gpk);
}
}
}
static void print_other_cpu_stall(unsigned long gp_seq)
{
int cpu;
unsigned long flags;
unsigned long gpa;
unsigned long j;
int ndetected = 0;
struct rcu_node *rnp;
long totqlen = 0;
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads();
if (rcu_cpu_stall_suppress)
return;
/*
* OK, time to rat on our buddy...
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
rcu_for_each_leaf_node(rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
ndetected += rcu_print_task_stall(rnp);
if (rnp->qsmask != 0) {
for_each_leaf_node_possible_cpu(rnp, cpu)
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
print_cpu_stall_info(cpu);
ndetected++;
}
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
for_each_possible_cpu(cpu)
totqlen += rcu_get_n_cbs_cpu(cpu);
pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
if (ndetected) {
rcu_dump_cpu_stacks();
/* Complain about tasks blocking the grace period. */
rcu_for_each_leaf_node(rnp)
rcu_print_detail_task_stall_rnp(rnp);
} else {
if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
pr_err("INFO: Stall ended before state dump start\n");
} else {
j = jiffies;
gpa = READ_ONCE(rcu_state.gp_activity);
pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
rcu_state.name, j - gpa, j, gpa,
READ_ONCE(jiffies_till_next_fqs),
rcu_get_root()->qsmask);
/* In this case, the current CPU might be at fault. */
sched_show_task(current);
}
}
/* Rewrite if needed in case of slow consoles. */
if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
WRITE_ONCE(rcu_state.jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
rcu_check_gp_kthread_starvation();
panic_on_rcu_stall();
rcu_force_quiescent_state(); /* Kick them all. */
}
static void print_cpu_stall(void)
{
int cpu;
unsigned long flags;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rcu_get_root();
long totqlen = 0;
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads();
if (rcu_cpu_stall_suppress)
return;
/*
* OK, time to rat on ourselves...
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
print_cpu_stall_info(smp_processor_id());
raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
for_each_possible_cpu(cpu)
totqlen += rcu_get_n_cbs_cpu(cpu);
pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
jiffies - rcu_state.gp_start,
(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
rcu_check_gp_kthread_starvation();
rcu_dump_cpu_stacks();
raw_spin_lock_irqsave_rcu_node(rnp, flags);
/* Rewrite if needed in case of slow consoles. */
if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
WRITE_ONCE(rcu_state.jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
panic_on_rcu_stall();
/*
* Attempt to revive the RCU machinery by forcing a context switch.
*
* A context switch would normally allow the RCU state machine to make
* progress and it could be we're stuck in kernel space without context
* switches for an entirely unreasonable amount of time.
*/
set_tsk_need_resched(current);
set_preempt_need_resched();
}
static void check_cpu_stall(struct rcu_data *rdp)
{
unsigned long gs1;
unsigned long gs2;
unsigned long gps;
unsigned long j;
unsigned long jn;
unsigned long js;
struct rcu_node *rnp;
if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
!rcu_gp_in_progress())
return;
rcu_stall_kick_kthreads();
j = jiffies;
/*
* Lots of memory barriers to reject false positives.
*
* The idea is to pick up rcu_state.gp_seq, then
* rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
* another copy of rcu_state.gp_seq. These values are updated in
* the opposite order with memory barriers (or equivalent) during
* grace-period initialization and cleanup. Now, a false positive
* can occur if we get an new value of rcu_state.gp_start and a old
* value of rcu_state.jiffies_stall. But given the memory barriers,
* the only way that this can happen is if one grace period ends
* and another starts between these two fetches. This is detected
* by comparing the second fetch of rcu_state.gp_seq with the
* previous fetch from rcu_state.gp_seq.
*
* Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
* and rcu_state.gp_start suffice to forestall false positives.
*/
gs1 = READ_ONCE(rcu_state.gp_seq);
smp_rmb(); /* Pick up ->gp_seq first... */
js = READ_ONCE(rcu_state.jiffies_stall);
smp_rmb(); /* ...then ->jiffies_stall before the rest... */
gps = READ_ONCE(rcu_state.gp_start);
smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
gs2 = READ_ONCE(rcu_state.gp_seq);
if (gs1 != gs2 ||
ULONG_CMP_LT(j, js) ||
ULONG_CMP_GE(gps, js))
return; /* No stall or GP completed since entering function. */
rnp = rdp->mynode;
jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
if (rcu_gp_in_progress() &&
(READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
/* We haven't checked in, so go dump stack. */
print_cpu_stall();
} else if (rcu_gp_in_progress() &&
ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
/* They had a few time units to dump stack, so complain. */
print_other_cpu_stall(gs2);
}
}
//////////////////////////////////////////////////////////////////////////////
//
// RCU forward-progress mechanisms, including of callback invocation.
/*
* Show the state of the grace-period kthreads.
*/
void show_rcu_gp_kthreads(void)
{
int cpu;
unsigned long j;
unsigned long ja;
unsigned long jr;
unsigned long jw;
struct rcu_data *rdp;
struct rcu_node *rnp;
j = jiffies;
ja = j - READ_ONCE(rcu_state.gp_activity);
jr = j - READ_ONCE(rcu_state.gp_req_activity);
jw = j - READ_ONCE(rcu_state.gp_wake_time);
pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
rcu_state.name, gp_state_getname(rcu_state.gp_state),
rcu_state.gp_state,
rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
(long)READ_ONCE(rcu_state.gp_seq),
(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
READ_ONCE(rcu_state.gp_flags));
rcu_for_each_node_breadth_first(rnp) {
if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
continue;
pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
rnp->grplo, rnp->grphi, (long)rnp->gp_seq,
(long)rnp->gp_seq_needed);
if (!rcu_is_leaf_node(rnp))
continue;
for_each_leaf_node_possible_cpu(rnp, cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rdp->gpwrap ||
ULONG_CMP_GE(rcu_state.gp_seq,
rdp->gp_seq_needed))
continue;
pr_info("\tcpu %d ->gp_seq_needed %ld\n",
cpu, (long)rdp->gp_seq_needed);
}
}
/* sched_show_task(rcu_state.gp_kthread); */
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
/*
* This function checks for grace-period requests that fail to motivate
* RCU to come out of its idle mode.
*/
static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
const unsigned long gpssdelay)
{
unsigned long flags;
unsigned long j;
struct rcu_node *rnp_root = rcu_get_root();
static atomic_t warned = ATOMIC_INIT(0);
if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
return;
j = jiffies; /* Expensive access, and in common case don't get here. */
if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
atomic_read(&warned))
return;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
j = jiffies;
if (rcu_gp_in_progress() ||
ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
atomic_read(&warned)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
/* Hold onto the leaf lock to make others see warned==1. */
if (rnp_root != rnp)
raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
j = jiffies;
if (rcu_gp_in_progress() ||
ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
time_before(j, rcu_state.gp_activity + gpssdelay) ||
atomic_xchg(&warned, 1)) {
if (rnp_root != rnp)
/* irqs remain disabled. */
raw_spin_unlock_rcu_node(rnp_root);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
WARN_ON(1);
if (rnp_root != rnp)
raw_spin_unlock_rcu_node(rnp_root);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
show_rcu_gp_kthreads();
}
/*
* Do a forward-progress check for rcutorture. This is normally invoked
* due to an OOM event. The argument "j" gives the time period during
* which rcutorture would like progress to have been made.
*/
void rcu_fwd_progress_check(unsigned long j)
{
unsigned long cbs;
int cpu;
unsigned long max_cbs = 0;
int max_cpu = -1;
struct rcu_data *rdp;
if (rcu_gp_in_progress()) {
pr_info("%s: GP age %lu jiffies\n",
__func__, jiffies - rcu_state.gp_start);
show_rcu_gp_kthreads();
} else {
pr_info("%s: Last GP end %lu jiffies ago\n",
__func__, jiffies - rcu_state.gp_end);
preempt_disable();
rdp = this_cpu_ptr(&rcu_data);
rcu_check_gp_start_stall(rdp->mynode, rdp, j);
preempt_enable();
}
for_each_possible_cpu(cpu) {
cbs = rcu_get_n_cbs_cpu(cpu);
if (!cbs)
continue;
if (max_cpu < 0)
pr_info("%s: callbacks", __func__);
pr_cont(" %d: %lu", cpu, cbs);
if (cbs <= max_cbs)
continue;
max_cbs = cbs;
max_cpu = cpu;
}
if (max_cpu >= 0)
pr_cont("\n");
}
EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
/* Commandeer a sysrq key to dump RCU's tree. */
static bool sysrq_rcu;
module_param(sysrq_rcu, bool, 0444);
/* Dump grace-period-request information due to commandeered sysrq. */
static void sysrq_show_rcu(int key)
{
show_rcu_gp_kthreads();
}
static struct sysrq_key_op sysrq_rcudump_op = {
.handler = sysrq_show_rcu,
.help_msg = "show-rcu(y)",
.action_msg = "Show RCU tree",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
static int __init rcu_sysrq_init(void)
{
if (sysrq_rcu)
return register_sysrq_key('y', &sysrq_rcudump_op);
return 0;
}
early_initcall(rcu_sysrq_init);
