rcu: Remove CONFIG_RCU_CPU_STALL_INFO

The CONFIG_RCU_CPU_STALL_INFO has been default-y for a couple of
releases with no complaints, so it is time to eliminate this Kconfig
option entirely, so that the long-form RCU CPU stall warnings cannot
be disabled.  This commit does just that.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Documentation/RCU/stallwarn.txt

@@ -26,12 +26,6 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
 	Stall-warning messages may be enabled and disabled completely via
 	/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.
 
-CONFIG_RCU_CPU_STALL_INFO
-
-	This kernel configuration parameter causes the stall warning to
-	print out additional per-CPU diagnostic information, including
-	information on scheduling-clock ticks and RCU's idle-CPU tracking.
-
 RCU_STALL_DELAY_DELTA
 
 	Although the lockdep facility is extremely useful, it does add
@@ -101,15 +95,13 @@ interact.  Please note that it is not possible to entirely eliminate this
 sort of false positive without resorting to things like stop_machine(),
 which is overkill for this sort of problem.
 
-If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
-more information is printed with the stall-warning message, for example:
+Recent kernels will print a long form of the stall-warning message:
 
 	INFO: rcu_preempt detected stall on CPU
 	0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 softirq=82/543
 	   (t=65000 jiffies)
 
-In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is
-printed:
+In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed:
 
 	INFO: rcu_preempt detected stall on CPU
 	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D

kernel/rcu/tree.h

@@ -288,12 +288,10 @@ struct rcu_data {
 	bool		gpwrap;		/* Possible gpnum/completed wrap. */
 	struct rcu_node *mynode;	/* This CPU's leaf of hierarchy */
 	unsigned long grpmask;		/* Mask to apply to leaf qsmask. */
-#ifdef CONFIG_RCU_CPU_STALL_INFO
 	unsigned long	ticks_this_gp;	/* The number of scheduling-clock */
 					/*  ticks this CPU has handled */
 					/*  during and after the last grace */
 					/* period it is aware of. */
-#endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
 
 	/* 2) batch handling */
 	/*
@@ -388,9 +386,7 @@ struct rcu_data {
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 
 	/* 8) RCU CPU stall data. */
-#ifdef CONFIG_RCU_CPU_STALL_INFO
 	unsigned int softirq_snap;	/* Snapshot of softirq activity. */
-#endif /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
 
 	int cpu;
 	struct rcu_state *rsp;

kernel/rcu/tree_plugin.h

@@ -82,8 +82,6 @@ static void __init rcu_bootup_announce_oddness(void)
 		pr_info("\tRCU lockdep checking is enabled.\n");
 	if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE))
 		pr_info("\tRCU torture testing starts during boot.\n");
-	if (IS_ENABLED(CONFIG_RCU_CPU_STALL_INFO))
-		pr_info("\tAdditional per-CPU info printed with stalls.\n");
 	if (RCU_NUM_LVLS >= 4)
 		pr_info("\tFour(or more)-level hierarchy is enabled.\n");
 	if (RCU_FANOUT_LEAF != 16)
@@ -418,8 +416,6 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp)
 		rcu_print_detail_task_stall_rnp(rnp);
 }
 
-#ifdef CONFIG_RCU_CPU_STALL_INFO
-
 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
 {
 	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
@@ -431,18 +427,6 @@ static void rcu_print_task_stall_end(void)
 	pr_cont("\n");
 }
 
-#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
-
-static void rcu_print_task_stall_begin(struct rcu_node *rnp)
-{
-}
-
-static void rcu_print_task_stall_end(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
-
 /*
  * Scan the current list of tasks blocked within RCU read-side critical
  * sections, printing out the tid of each.
@@ -1685,8 +1669,6 @@ early_initcall(rcu_register_oom_notifier);
 
 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
 
-#ifdef CONFIG_RCU_CPU_STALL_INFO
-
 #ifdef CONFIG_RCU_FAST_NO_HZ
 
 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
@@ -1775,33 +1757,6 @@ static void increment_cpu_stall_ticks(void)
 		raw_cpu_inc(rsp->rda->ticks_this_gp);
 }
 
-#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
-
-static void print_cpu_stall_info_begin(void)
-{
-	pr_cont(" {");
-}
-
-static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
-{
-	pr_cont(" %d", cpu);
-}
-
-static void print_cpu_stall_info_end(void)
-{
-	pr_cont("} ");
-}
-
-static void zero_cpu_stall_ticks(struct rcu_data *rdp)
-{
-}
-
-static void increment_cpu_stall_ticks(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
-
 #ifdef CONFIG_RCU_NOCB_CPU
 
 /*

lib/Kconfig.debug

@@ -1353,20 +1353,6 @@ config RCU_CPU_STALL_TIMEOUT
 	  RCU grace period persists, additional CPU stall warnings are
 	  printed at more widely spaced intervals.
 
-config RCU_CPU_STALL_INFO
-	bool "Print additional diagnostics on RCU CPU stall"
-	depends on (TREE_RCU || PREEMPT_RCU) && DEBUG_KERNEL
-	default y
-	help
-	  For each stalled CPU that is aware of the current RCU grace
-	  period, print out additional per-CPU diagnostic information
-	  regarding scheduling-clock ticks, idle state, and,
-	  for RCU_FAST_NO_HZ kernels, idle-entry state.
-
-	  Say N if you are unsure.
-
-	  Say Y if you want to enable such diagnostics.
-
 config RCU_TRACE
 	bool "Enable tracing for RCU"
 	depends on DEBUG_KERNEL

tools/testing/selftests/rcutorture/configs/rcu/TREE01

@@ -13,7 +13,6 @@ CONFIG_MAXSMP=y
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_RCU_NOCB_CPU_ZERO=y
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE02

@@ -17,7 +17,6 @@ CONFIG_RCU_FANOUT_LEAF=3
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE02-T

@@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT_LEAF=3
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

tools/testing/selftests/rcutorture/configs/rcu/TREE03

@@ -13,7 +13,6 @@ CONFIG_RCU_FANOUT=2
 CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=y
 CONFIG_RCU_KTHREAD_PRIO=2
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

tools/testing/selftests/rcutorture/configs/rcu/TREE04

@@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT=4
 CONFIG_RCU_FANOUT_LEAF=4
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE05

@@ -17,6 +17,5 @@ CONFIG_RCU_NOCB_CPU_NONE=y
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE06

@@ -18,6 +18,5 @@ CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE07

@@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT=2
 CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE08

@@ -19,7 +19,6 @@ CONFIG_RCU_NOCB_CPU_ALL=y
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE08-T

@@ -17,6 +17,5 @@ CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_RCU_NOCB_CPU_ALL=y
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n

tools/testing/selftests/rcutorture/configs/rcu/TREE09

@@ -13,7 +13,6 @@ CONFIG_SUSPEND=n
 CONFIG_HIBERNATION=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_CPU_STALL_INFO=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 #CHECK#CONFIG_RCU_EXPERT=n

tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt

@@ -16,7 +16,6 @@ CONFIG_PROVE_LOCKING -- Do several, covering CONFIG_DEBUG_LOCK_ALLOC=y and not.
 CONFIG_PROVE_RCU -- Hardwired to CONFIG_PROVE_LOCKING.
 CONFIG_RCU_BOOST -- one of PREEMPT_RCU.
 CONFIG_RCU_KTHREAD_PRIO -- set to 2 for _BOOST testing.
-CONFIG_RCU_CPU_STALL_INFO -- Now default, avoid at least twice.
 CONFIG_RCU_FANOUT -- Cover hierarchy, but overlap with others.
 CONFIG_RCU_FANOUT_LEAF -- Do one non-default.
 CONFIG_RCU_FAST_NO_HZ -- Do one, but not with CONFIG_RCU_NOCB_CPU_ALL.