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rcu: Allow expedited RCU CPU stall warnings to dump task stacks

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This commit introduces the rcupdate.rcu_exp_stall_task_details kernel
boot parameter, which cause expedited RCU CPU stall warnings to dump
the stacks of any tasks blocking the current expedited grace period.

Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-12-19 18:02:20 -08:00
parent 748bf47a89
commit 92987fe8bd
4 changed files with 49 additions and 0 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@ -5113,6 +5113,11 @@
rcupdate.rcu_cpu_stall_timeout to be used (after
conversion from seconds to milliseconds).
rcupdate.rcu_exp_stall_task_details= [KNL]
Print stack dumps of any tasks blocking the
current expedited RCU grace period during an
expedited RCU CPU stall warning.
rcupdate.rcu_expedited= [KNL]
Use expedited grace-period primitives, for
example, synchronize_rcu_expedited() instead

1
kernel/rcu/rcu.h
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@ -224,6 +224,7 @@ extern int rcu_cpu_stall_ftrace_dump;
extern int rcu_cpu_stall_suppress;
extern int rcu_cpu_stall_timeout;
extern int rcu_exp_cpu_stall_timeout;
extern bool rcu_exp_stall_task_details __read_mostly;
int rcu_jiffies_till_stall_check(void);
int rcu_exp_jiffies_till_stall_check(void);

41
kernel/rcu/tree_exp.h
View File

@ -11,6 +11,7 @@
static void rcu_exp_handler(void *unused);
static int rcu_print_task_exp_stall(struct rcu_node *rnp);
static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp);
/*
* Record the start of an expedited grace period.
@ -671,6 +672,7 @@ static void synchronize_rcu_expedited_wait(void)
dump_cpu_task(cpu);
preempt_enable();
}
rcu_exp_print_detail_task_stall_rnp(rnp);
}
jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
panic_on_rcu_stall();
@ -813,6 +815,36 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
return ndetected;
}
/*
* Scan the current list of tasks blocked within RCU read-side critical
* sections, dumping the stack of each that is blocking the current
* expedited grace period.
*/
static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
unsigned long flags;
struct task_struct *t;
if (!rcu_exp_stall_task_details)
return;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (!READ_ONCE(rnp->exp_tasks)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
t = list_entry(rnp->exp_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);
}
#else /* #ifdef CONFIG_PREEMPT_RCU */
/* Request an expedited quiescent state. */
@ -885,6 +917,15 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
return 0;
}
/*
* Because preemptible RCU does not exist, we never have to print out
* tasks blocked within RCU read-side critical sections that are blocking
* the current expedited grace period.
*/
static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/**

2
kernel/rcu/update.c
View File

@ -509,6 +509,8 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
module_param(rcu_cpu_stall_timeout, int, 0644);
int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
module_param(rcu_exp_cpu_stall_timeout, int, 0644);
bool rcu_exp_stall_task_details __read_mostly;
module_param(rcu_exp_stall_task_details, bool, 0644);
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall