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Commit 910b1b7e authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Allow RCU CPU stall warnings to be off at boot, but manually enablable 



Currently, if RCU CPU stall warnings are enabled, they are enabled
immediately upon boot.  They can be manually disabled via /sys (and
also re-enabled via /sys), and are automatically disabled upon panic.
However, some users need RCU CPU stalls to be disabled at boot time,
but to be enabled without rebuilding/rebooting.  For example, someone
running a real-time application in production might not want the
additional latency of RCU CPU stall detection in normal operation, but
might need to enable it at any point for fault isolation purposes.

This commit therefore provides a new CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE
kernel configuration parameter that maintains the current behavior
(enable at boot) by default, but allows a kernel to be configured
with RCU CPU stall detection built into the kernel, but disabled at
boot time.

Requested-by: default avatarClark Williams <williams@redhat.com>
Requested-by: default avatarJohn Kacur <jkacur@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 687d7a96

kernel/rcutree.c

+1 −1
Original line number Diff line number Diff line
@@ -144,7 +144,7 @@ module_param(qhimark, int, 0); 
module_param(qlowmark, int, 0);



#ifdef CONFIG_RCU_CPU_STALL_DETECTOR

int rcu_cpu_stall_suppress __read_mostly;

int rcu_cpu_stall_suppress __read_mostly = RCU_CPU_STALL_SUPPRESS_INIT;

module_param(rcu_cpu_stall_suppress, int, 0644);

#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */

kernel/rcutree.h

+6 −0
Original line number Diff line number Diff line
@@ -264,6 +264,12 @@ struct rcu_data { 
						/*  scheduling clock irq */

						/*  before ratting on them. */



#ifdef CONFIG_RCU_CPU_STALL_DETECTOR_RUNNABLE

#define RCU_CPU_STALL_SUPPRESS_INIT 0

#else

#define RCU_CPU_STALL_SUPPRESS_INIT 1

#endif



#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */



#define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))

lib/Kconfig.debug

+13 −0
Original line number Diff line number Diff line
@@ -856,6 +856,19 @@ config RCU_CPU_STALL_TIMEOUT 
	  RCU grace period persists, additional CPU stall warnings are

	  printed at more widely spaced intervals.



config RCU_CPU_STALL_DETECTOR_RUNNABLE

	bool "RCU CPU stall checking starts automatically at boot"

	depends on RCU_CPU_STALL_DETECTOR

	default y

	help

	  If set, start checking for RCU CPU stalls immediately on

	  boot.  Otherwise, RCU CPU stall checking must be manually

	  enabled.



	  Say Y if you are unsure.



	  Say N if you wish to suppress RCU CPU stall checking during boot.



config RCU_CPU_STALL_VERBOSE

	bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"

	depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU