Commit 92987fe8 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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



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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 748bf47a

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcu/rcu.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

kernel/rcu/tree_exp.h

+41 −0
Original line number Diff line number Diff line
@@ -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 */



/**

kernel/rcu/update.c

+2 −0
Original line number Diff line number Diff line
@@ -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