Merge tag 'rcu.2022.05.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU update from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes

 - Callback-offloading updates, mainly simplifications

 - RCU-tasks updates, including some -rt fixups, handling of systems
   with sparse CPU numbering, and a fix for a boot-time race-condition
   failure

 - Put SRCU on a memory diet in order to reduce the size of the
   srcu_struct structure

 - Torture-test updates fixing some bugs in tests and closing some
   testing holes

 - Torture-test updates for the RCU tasks flavors, most notably ensuring
   that building rcutorture and friends does not change the
   RCU-tasks-related Kconfig options

 - Torture-test scripting updates

 - Expedited grace-period updates, most notably providing
   milliseconds-scale (not all that) soft real-time response from
   synchronize_rcu_expedited().

   This is also the first time in almost 30 years of RCU that someone
   other than me has pushed for a reduction in the RCU CPU stall-warning
   timeout, in this case by more than three orders of magnitude from 21
   seconds to 20 milliseconds. This tighter timeout applies only to
   expedited grace periods

* tag 'rcu.2022.05.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (80 commits)
  rcu: Move expedited grace period (GP) work to RT kthread_worker
  rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
  srcu: Drop needless initialization of sdp in srcu_gp_start()
  srcu: Prevent expedited GPs and blocking readers from consuming CPU
  srcu: Add contention check to call_srcu() srcu_data ->lock acquisition
  srcu: Automatically determine size-transition strategy at boot
  rcutorture: Make torture.sh allow for --kasan
  rcutorture: Make torture.sh refscale and rcuscale specify Tasks Trace RCU
  rcutorture: Make kvm.sh allow more memory for --kasan runs
  torture: Save "make allmodconfig" .config file
  scftorture: Remove extraneous "scf" from per_version_boot_params
  rcutorture: Adjust scenarios' Kconfig options for CONFIG_PREEMPT_DYNAMIC
  torture: Enable CSD-lock stall reports for scftorture
  torture: Skip vmlinux check for kvm-again.sh runs
  scftorture: Adjust for TASKS_RCU Kconfig option being selected
  rcuscale: Allow rcuscale without RCU Tasks Rude/Trace
  rcuscale: Allow rcuscale without RCU Tasks
  refscale: Allow refscale without RCU Tasks Rude/Trace
  refscale: Allow refscale without RCU Tasks
  rcutorture: Allow specifying per-scenario stat_interval
  ...

4 files changed, 68 insertions, 8 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e7c39c200e2b..1a32036c918c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -196,6 +196,7 @@ void synchronize_rcu_tasks_rude(void);
 void exit_tasks_rcu_start(void);
 void exit_tasks_rcu_finish(void);
 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
+#define rcu_tasks_classic_qs(t, preempt) do { } while (0)
 #define rcu_tasks_qs(t, preempt) do { } while (0)
 #define rcu_note_voluntary_context_switch(t) do { } while (0)
 #define call_rcu_tasks call_rcu
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a8911b1f35aa..b3278f8184d5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2118,6 +2118,47 @@ static inline void cond_resched_rcu(void)
 #endif
 }
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+extern bool preempt_model_none(void);
+extern bool preempt_model_voluntary(void);
+extern bool preempt_model_full(void);
+
+#else
+
+static inline bool preempt_model_none(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_NONE);
+}
+static inline bool preempt_model_voluntary(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY);
+}
+static inline bool preempt_model_full(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT);
+}
+
+#endif
+
+static inline bool preempt_model_rt(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_RT);
+}
+
+/*
+ * Does the preemption model allow non-cooperative preemption?
+ *
+ * For !CONFIG_PREEMPT_DYNAMIC kernels this is an exact match with
+ * CONFIG_PREEMPTION; for CONFIG_PREEMPT_DYNAMIC this doesn't work as the
+ * kernel is *built* with CONFIG_PREEMPTION=y but may run with e.g. the
+ * PREEMPT_NONE model.
+ */
+static inline bool preempt_model_preemptible(void)
+{
+	return preempt_model_full() || preempt_model_rt();
+}
+
 /*
  * Does a critical section need to be broken due to another
  * task waiting?: (technically does not depend on CONFIG_PREEMPTION,
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index cb1f4351e8ba..e3014319d1ad 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -47,11 +47,9 @@ struct srcu_data {
  */
 struct srcu_node {
 	spinlock_t __private lock;
-	unsigned long srcu_have_cbs[4];		/* GP seq for children */
-						/*  having CBs, but only */
-						/*  is > ->srcu_gq_seq. */
-	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs */
-						/*  have CBs for given GP? */
+	unsigned long srcu_have_cbs[4];		/* GP seq for children having CBs, but only */
+						/*  if greater than ->srcu_gq_seq. */
+	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs have CBs for given GP? */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	struct srcu_node *srcu_parent;		/* Next up in tree. */
 	int grplo;				/* Least CPU for node. */
@@ -62,18 +60,24 @@ struct srcu_node {
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
-	struct srcu_node node[NUM_RCU_NODES];	/* Combining tree. */
+	struct srcu_node *node;			/* Combining tree. */
 	struct srcu_node *level[RCU_NUM_LVLS + 1];
 						/* First node at each level. */
+	int srcu_size_state;			/* Small-to-big transition state. */
 	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
-	spinlock_t __private lock;		/* Protect counters */
+	spinlock_t __private lock;		/* Protect counters and size state. */
 	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
 	unsigned int srcu_idx;			/* Current rdr array element. */
 	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
 	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
+	unsigned long srcu_gp_start;		/* Last GP start timestamp (jiffies) */
 	unsigned long srcu_last_gp_end;		/* Last GP end timestamp (ns) */
+	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
+	unsigned long srcu_n_lock_retries;	/* Contention events in current interval. */
+	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
+	bool sda_is_static;			/* May ->sda be passed to free_percpu()? */
 	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
 	struct mutex srcu_barrier_mutex;	/* Serialize barrier ops. */
 	struct completion srcu_barrier_completion;
@@ -81,10 +85,23 @@ struct srcu_struct {
 	atomic_t srcu_barrier_cpu_cnt;		/* # CPUs not yet posting a */
 						/*  callback for the barrier */
 						/*  operation. */
+	unsigned long reschedule_jiffies;
+	unsigned long reschedule_count;
 	struct delayed_work work;
 	struct lockdep_map dep_map;
 };
 
+/* Values for size state variable (->srcu_size_state). */
+#define SRCU_SIZE_SMALL		0
+#define SRCU_SIZE_ALLOC		1
+#define SRCU_SIZE_WAIT_BARRIER	2
+#define SRCU_SIZE_WAIT_CALL	3
+#define SRCU_SIZE_WAIT_CBS1	4
+#define SRCU_SIZE_WAIT_CBS2	5
+#define SRCU_SIZE_WAIT_CBS3	6
+#define SRCU_SIZE_WAIT_CBS4	7
+#define SRCU_SIZE_BIG		8
+
 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
@@ -121,6 +138,7 @@ struct srcu_struct {
 #ifdef MODULE
 # define __DEFINE_SRCU(name, is_static)					\
 	is_static struct srcu_struct name;				\
+	extern struct srcu_struct * const __srcu_struct_##name;		\
 	struct srcu_struct * const __srcu_struct_##name			\
 		__section("___srcu_struct_ptrs") = &name
 #else
diff --git a/include/linux/torture.h b/include/linux/torture.h
index 63fa4196e51c..7038104463e4 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -118,7 +118,7 @@ void _torture_stop_kthread(char *m, struct task_struct **tp);
 	_torture_stop_kthread("Stopping " #n " task", &(tp))
 
 #ifdef CONFIG_PREEMPTION
-#define torture_preempt_schedule() preempt_schedule()
+#define torture_preempt_schedule() __preempt_schedule()
 #else
 #define torture_preempt_schedule()	do { } while (0)
 #endif