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rcu: Add sysrq rcu_node-dump capability

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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: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-12-12 12:32:06 -08:00
parent 3b6505fd8e
commit 2ccaff10f7
2 changed files with 30 additions and 0 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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().

25
kernel/rcu/tree.c
View File

@ -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.
*/