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-rw-r--r--Documentation/admin-guide/kernel-parameters.txt6
-rw-r--r--include/linux/rcu_notifier.h6
-rw-r--r--kernel/rcu/Kconfig.debug25
-rw-r--r--kernel/rcu/rcu.h8
-rw-r--r--kernel/rcu/rcutorture.c12
-rw-r--r--kernel/rcu/tree_stall.h11
-rw-r--r--kernel/rcu/update.c6
7 files changed, 62 insertions, 12 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 65731b060e3f..b72e2049c487 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5302,6 +5302,12 @@
Dump ftrace buffer after reporting RCU CPU
stall warning.
+ rcupdate.rcu_cpu_stall_notifiers= [KNL]
+ Provide RCU CPU stall notifiers, but see the
+ warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
+ option's help text. TL;DR: You almost certainly
+ do not want rcupdate.rcu_cpu_stall_notifiers.
+
rcupdate.rcu_cpu_stall_suppress= [KNL]
Suppress RCU CPU stall warning messages.
diff --git a/include/linux/rcu_notifier.h b/include/linux/rcu_notifier.h
index ebf371364581..5640f024773b 100644
--- a/include/linux/rcu_notifier.h
+++ b/include/linux/rcu_notifier.h
@@ -13,7 +13,7 @@
#define RCU_STALL_NOTIFY_NORM 1
#define RCU_STALL_NOTIFY_EXP 2
-#ifdef CONFIG_RCU_STALL_COMMON
+#if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
#include <linux/notifier.h>
#include <linux/types.h>
@@ -21,12 +21,12 @@
int rcu_stall_chain_notifier_register(struct notifier_block *n);
int rcu_stall_chain_notifier_unregister(struct notifier_block *n);
-#else // #ifdef CONFIG_RCU_STALL_COMMON
+#else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
// No RCU CPU stall warnings in Tiny RCU.
static inline int rcu_stall_chain_notifier_register(struct notifier_block *n) { return -EEXIST; }
static inline int rcu_stall_chain_notifier_unregister(struct notifier_block *n) { return -ENOENT; }
-#endif // #else // #ifdef CONFIG_RCU_STALL_COMMON
+#endif // #else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
#endif /* __LINUX_RCU_NOTIFIER_H */
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 2984de629f74..9b0b52e1836f 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -105,6 +105,31 @@ config RCU_CPU_STALL_CPUTIME
The boot option rcupdate.rcu_cpu_stall_cputime has the same function
as this one, but will override this if it exists.
+config RCU_CPU_STALL_NOTIFIER
+ bool "Provide RCU CPU-stall notifiers"
+ depends on RCU_STALL_COMMON
+ depends on DEBUG_KERNEL
+ depends on RCU_EXPERT
+ default n
+ help
+ WARNING: You almost certainly do not want this!!!
+
+ Enable RCU CPU-stall notifiers, which are invoked just before
+ printing the RCU CPU stall warning. As such, bugs in notifier
+ callbacks can prevent stall warnings from being printed.
+ And the whole reason that a stall warning is being printed is
+ that something is hung up somewhere. Therefore, the notifier
+ callbacks must be written extremely carefully, preferably
+ containing only lockless code. After all, it is quite possible
+ that the whole reason that the RCU CPU stall is happening in
+ the first place is that someone forgot to release whatever lock
+ that you are thinking of acquiring. In which case, having your
+ notifier callback acquire that lock will hang, preventing the
+ RCU CPU stall warning from appearing.
+
+ Say Y here if you want RCU CPU stall notifiers (you don't want them)
+ Say N if you are unsure.
+
config RCU_TRACE
bool "Enable tracing for RCU"
depends on DEBUG_KERNEL
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index b531c33e9545..f94f65877f2b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -262,6 +262,8 @@ static inline bool rcu_stall_is_suppressed_at_boot(void)
return rcu_cpu_stall_suppress_at_boot && !rcu_inkernel_boot_has_ended();
}
+extern int rcu_cpu_stall_notifiers;
+
#ifdef CONFIG_RCU_STALL_COMMON
extern int rcu_cpu_stall_ftrace_dump;
@@ -659,10 +661,10 @@ static inline bool rcu_cpu_beenfullyonline(int cpu) { return true; }
bool rcu_cpu_beenfullyonline(int cpu);
#endif
-#ifdef CONFIG_RCU_STALL_COMMON
+#if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
int rcu_stall_notifier_call_chain(unsigned long val, void *v);
-#else // #ifdef CONFIG_RCU_STALL_COMMON
+#else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
static inline int rcu_stall_notifier_call_chain(unsigned long val, void *v) { return NOTIFY_DONE; }
-#endif // #else // #ifdef CONFIG_RCU_STALL_COMMON
+#endif // #else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER)
#endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 30fc9d34e329..07a6a183c555 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2450,10 +2450,12 @@ static int rcu_torture_stall(void *args)
unsigned long stop_at;
VERBOSE_TOROUT_STRING("rcu_torture_stall task started");
- ret = rcu_stall_chain_notifier_register(&rcu_torture_stall_block);
- if (ret)
- pr_info("%s: rcu_stall_chain_notifier_register() returned %d, %sexpected.\n",
- __func__, ret, !IS_ENABLED(CONFIG_RCU_STALL_COMMON) ? "un" : "");
+ if (rcu_cpu_stall_notifiers) {
+ ret = rcu_stall_chain_notifier_register(&rcu_torture_stall_block);
+ if (ret)
+ pr_info("%s: rcu_stall_chain_notifier_register() returned %d, %sexpected.\n",
+ __func__, ret, !IS_ENABLED(CONFIG_RCU_STALL_COMMON) ? "un" : "");
+ }
if (stall_cpu_holdoff > 0) {
VERBOSE_TOROUT_STRING("rcu_torture_stall begin holdoff");
schedule_timeout_interruptible(stall_cpu_holdoff * HZ);
@@ -2497,7 +2499,7 @@ static int rcu_torture_stall(void *args)
cur_ops->readunlock(idx);
}
pr_alert("%s end.\n", __func__);
- if (!ret) {
+ if (rcu_cpu_stall_notifiers && !ret) {
ret = rcu_stall_chain_notifier_unregister(&rcu_torture_stall_block);
if (ret)
pr_info("%s: rcu_stall_chain_notifier_unregister() returned %d.\n", __func__, ret);
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index ac8e86babe44..5d666428546b 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -1061,6 +1061,7 @@ static int __init rcu_sysrq_init(void)
}
early_initcall(rcu_sysrq_init);
+#ifdef CONFIG_RCU_CPU_STALL_NOTIFIER
//////////////////////////////////////////////////////////////////////////////
//
@@ -1081,7 +1082,13 @@ static ATOMIC_NOTIFIER_HEAD(rcu_cpu_stall_notifier_list);
*/
int rcu_stall_chain_notifier_register(struct notifier_block *n)
{
- return atomic_notifier_chain_register(&rcu_cpu_stall_notifier_list, n);
+ int rcsn = rcu_cpu_stall_notifiers;
+
+ WARN(1, "Adding %pS() to RCU stall notifier list (%s).\n", n->notifier_call,
+ rcsn ? "possibly suppressing RCU CPU stall warnings" : "failed, so all is well");
+ if (rcsn)
+ return atomic_notifier_chain_register(&rcu_cpu_stall_notifier_list, n);
+ return -EEXIST;
}
EXPORT_SYMBOL_GPL(rcu_stall_chain_notifier_register);
@@ -1115,3 +1122,5 @@ int rcu_stall_notifier_call_chain(unsigned long val, void *v)
{
return atomic_notifier_call_chain(&rcu_cpu_stall_notifier_list, val, v);
}
+
+#endif // #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c534d6806d3d..46aaaa9fe339 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -538,9 +538,15 @@ long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
EXPORT_SYMBOL_GPL(torture_sched_setaffinity);
#endif
+int rcu_cpu_stall_notifiers __read_mostly; // !0 = provide stall notifiers (rarely useful)
+EXPORT_SYMBOL_GPL(rcu_cpu_stall_notifiers);
+
#ifdef CONFIG_RCU_STALL_COMMON
int rcu_cpu_stall_ftrace_dump __read_mostly;
module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
+#ifdef CONFIG_RCU_CPU_STALL_NOTIFIER
+module_param(rcu_cpu_stall_notifiers, int, 0444);
+#endif // #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER
int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
module_param(rcu_cpu_stall_suppress, int, 0644);
generated by cgit v1.2.3-70-g09d2 (git 2.47.1) at 2024-12-24 01:51:28 +0000