rcu: Allow RCU CPU stall warnings to be off at boot, but manually enablable (910b1b7e) · Commits · 戴 / test

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:

Clark Williams <williams@redhat.com> Requested-by:

John Kacur <jkacur@redhat.com> Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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

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