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rcu/nocb: Print no-CBs diagnostics when rcutorture writer unduly delayed 

This commit causes locking, sleeping, and callback state to be printed
for no-CBs CPUs when the rcutorture writer is delayed sufficiently for
rcutorture to complain.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-06-25 13:32:51 -07:00
parent 6aacd88d17
commit f7a81b12d6
4 changed files with 94 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
kernel/rcu/rcutorture.c
View File

@ -2176,6 +2176,7 @@ rcu_torture_cleanup(void)
return;
}
show_rcu_gp_kthreads();
rcu_torture_barrier_cleanup();
torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);
torture_stop_kthread(rcu_torture_stall, stall_task);

7
kernel/rcu/tree.h
View File

@ -212,7 +212,11 @@ struct rcu_data {
/* The following fields are used by GP kthread, hence own cacheline. */
raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;
struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */
bool nocb_gp_sleep; /* Is the nocb GP thread asleep? */
u8 nocb_gp_sleep; /* Is the nocb GP thread asleep? */
u8 nocb_gp_bypass; /* Found a bypass on last scan? */
u8 nocb_gp_gp; /* GP to wait for on last scan? */
unsigned long nocb_gp_seq; /* If so, ->gp_seq to wait for. */
unsigned long nocb_gp_loops; /* # passes through wait code. */
struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */
bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */
struct task_struct *nocb_cb_kthread;
@ -438,6 +442,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
static void rcu_spawn_cpu_nocb_kthread(int cpu);
static void __init rcu_spawn_nocb_kthreads(void);
static void show_rcu_nocb_state(struct rcu_data *rdp);
static void rcu_nocb_lock(struct rcu_data *rdp);
static void rcu_nocb_unlock(struct rcu_data *rdp);
static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,

82
kernel/rcu/tree_plugin.h
View File

@ -2021,6 +2021,9 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
rcu_gp_kthread_wake();
}
my_rdp->nocb_gp_bypass = bypass;
my_rdp->nocb_gp_gp = needwait_gp;
my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
if (bypass && !rcu_nocb_poll) {
// At least one child with non-empty ->nocb_bypass, so set
// timer in order to avoid stranding its callbacks.
@ -2055,6 +2058,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
}
my_rdp->nocb_gp_seq = -1;
WARN_ON(signal_pending(current));
}
@ -2071,6 +2075,7 @@ static int rcu_nocb_gp_kthread(void *arg)
struct rcu_data *rdp = arg;
for (;;) {
WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
nocb_gp_wait(rdp);
cond_resched_tasks_rcu_qs();
}
@ -2362,6 +2367,79 @@ void rcu_bind_current_to_nocb(void)
}
EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
/*
* Dump out nocb grace-period kthread state for the specified rcu_data
* structure.
*/
static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
{
struct rcu_node *rnp = rdp->mynode;
pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
rdp->cpu,
"kK"[!!rdp->nocb_gp_kthread],
"lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
"dD"[!!rdp->nocb_defer_wakeup],
"tT"[timer_pending(&rdp->nocb_timer)],
"bB"[timer_pending(&rdp->nocb_bypass_timer)],
"sS"[!!rdp->nocb_gp_sleep],
".W"[swait_active(&rdp->nocb_gp_wq)],
".W"[swait_active(&rnp->nocb_gp_wq[0])],
".W"[swait_active(&rnp->nocb_gp_wq[1])],
".B"[!!rdp->nocb_gp_bypass],
".G"[!!rdp->nocb_gp_gp],
(long)rdp->nocb_gp_seq,
rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
}
/* Dump out nocb kthread state for the specified rcu_data structure. */
static void show_rcu_nocb_state(struct rcu_data *rdp)
{
struct rcu_segcblist *rsclp = &rdp->cblist;
bool waslocked;
bool wastimer;
bool wassleep;
if (rdp->nocb_gp_rdp == rdp)
show_rcu_nocb_gp_state(rdp);
pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
rdp->cpu, rdp->nocb_gp_rdp->cpu,
"kK"[!!rdp->nocb_cb_kthread],
"bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
"cC"[!!atomic_read(&rdp->nocb_lock_contended)],
"lL"[raw_spin_is_locked(&rdp->nocb_lock)],
"sS"[!!rdp->nocb_cb_sleep],
".W"[swait_active(&rdp->nocb_cb_wq)],
jiffies - rdp->nocb_bypass_first,
jiffies - rdp->nocb_nobypass_last,
rdp->nocb_nobypass_count,
".D"[rcu_segcblist_ready_cbs(rsclp)],
".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
rcu_segcblist_n_cbs(&rdp->cblist));
/* It is OK for GP kthreads to have GP state. */
if (rdp->nocb_gp_rdp == rdp)
return;
waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
wastimer = timer_pending(&rdp->nocb_timer);
wassleep = swait_active(&rdp->nocb_gp_wq);
if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&
!waslocked && !wastimer && !wassleep)
return; /* Nothing untowards. */
pr_info(" !!! %c%c%c%c %c\n",
"lL"[waslocked],
"dD"[!!rdp->nocb_defer_wakeup],
"tT"[wastimer],
"sS"[!!rdp->nocb_gp_sleep],
".W"[wassleep]);
}
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
/* No ->nocb_lock to acquire. */
@ -2439,6 +2517,10 @@ static void __init rcu_spawn_nocb_kthreads(void)
{
}
static void show_rcu_nocb_state(struct rcu_data *rdp)
{
}
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
/*

5
kernel/rcu/tree_stall.h
View File

@ -589,6 +589,11 @@ void show_rcu_gp_kthreads(void)
cpu, (long)rdp->gp_seq_needed);
}
}
for_each_possible_cpu(cpu) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_segcblist_is_offloaded(&rdp->cblist))
show_rcu_nocb_state(rdp);
}
/* sched_show_task(rcu_state.gp_kthread); */
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);