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Commit 2ccaff10 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add sysrq rcu_node-dump capability 



Life is hard if RCU manages to get stuck without triggering RCU CPU
stall warnings or triggering the rcu_check_gp_start_stall() checks
for failing to start a grace period.  This commit therefore adds a
boot-time-selectable sysrq key (commandeering "y") that allows manually
dumping Tree RCU state.  The new rcutree.sysrq_rcu kernel boot parameter
must be set for this sysrq to be available.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 3b6505fd

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -3721,6 +3721,11 @@ 
			This wake_up() will be accompanied by a

			WARN_ONCE() splat and an ftrace_dump().



	rcutree.sysrq_rcu= [KNL]

			Commandeer a sysrq key to dump out Tree RCU's

			rcu_node tree with an eye towards determining

			why a new grace period has not yet started.



	rcuperf.gp_async= [KNL]

			Measure performance of asynchronous

			grace-period primitives such as call_rcu().

kernel/rcu/tree.c

+25 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ 
#include <linux/suspend.h>

#include <linux/ftrace.h>

#include <linux/tick.h>

#include <linux/sysrq.h>



#include "tree.h"

#include "rcu.h"
@@ -115,6 +116,9 @@ int num_rcu_lvl[] = NUM_RCU_LVL_INIT; 
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */

/* panic() on RCU Stall sysctl. */

int sysctl_panic_on_rcu_stall __read_mostly;

/* Commandeer a sysrq key to dump RCU's tree. */

static bool sysrq_rcu;

module_param(sysrq_rcu, bool, 0444);



/*

 * The rcu_scheduler_active variable is initialized to the value
@@ -577,6 +581,27 @@ void show_rcu_gp_kthreads(void) 
}

EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);



/* 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);



/*

 * Send along grace-period-related data for rcutorture diagnostics.

 */