Merge tag 'rcu.next.v6.10' of https://github.com/urezki/linux

Pull RCU updates from Uladzislau Rezki:

 - Fix a lockdep complain for lazy-preemptible kernel, remove redundant
   BH disable for TINY_RCU, remove redundant READ_ONCE() in tree.c, fix
   false positives KCSAN splat and fix buffer overflow in the
   print_cpu_stall_info().

 - Misc updates related to bpf, tracing and update the MAINTAINERS file.

 - An improvement of a normal synchronize_rcu() call in terms of
   latency. It maintains a separate track for sync. users only. This
   approach bypasses per-cpu nocb-lists thus sync-users do not depend on
   nocb-list length and how fast regular callbacks are processed.

 - RCU tasks: switch tasks RCU grace periods to sleep at TASK_IDLE
   priority, fix some comments, add some diagnostic warning to the
   exit_tasks_rcu_start() and fix a buffer overflow in the
   show_rcu_tasks_trace_gp_kthread().

 - RCU torture: Increase memory to guest OS, fix a Tasks Rude RCU
   testing, some updates for TREE09, dump mode information to debug GP
   kthread state, remove redundant READ_ONCE(), fix some comments about
   RCU_TORTURE_PIPE_LEN and pipe_count, remove some redundant pointer
   initialization, fix a hung splat task by when the rcutorture tests
   start to exit, fix invalid context warning, add '--do-kvfree'
   parameter to torture test and use slow register unregister callbacks
   only for rcutype test.

* tag 'rcu.next.v6.10' of https://github.com/urezki/linux: (48 commits)
  rcutorture: Use rcu_gp_slow_register/unregister() only for rcutype test
  torture: Scale --do-kvfree test time
  rcutorture: Fix invalid context warning when enable srcu barrier testing
  rcutorture: Make stall-tasks directly exit when rcutorture tests end
  rcutorture: Removing redundant function pointer initialization
  rcutorture: Make rcutorture support print rcu-tasks gp state
  rcutorture: Use the gp_kthread_dbg operation specified by cur_ops
  rcutorture: Re-use value stored to ->rtort_pipe_count instead of re-reading
  rcutorture: Fix rcu_torture_one_read() pipe_count overflow comment
  rcutorture: Remove extraneous rcu_torture_pipe_update_one() READ_ONCE()
  rcu: Allocate WQ with WQ_MEM_RECLAIM bit set
  rcu: Support direct wake-up of synchronize_rcu() users
  rcu: Add a trace event for synchronize_rcu_normal()
  rcu: Reduce synchronize_rcu() latency
  rcu: Fix buffer overflow in print_cpu_stall_info()
  rcu: Mollify sparse with RCU guard
  rcu-tasks: Fix show_rcu_tasks_trace_gp_kthread buffer overflow
  rcu-tasks: Fix the comments for tasks_rcu_exit_srcu_stall_timer
  rcu-tasks: Replace exit_tasks_rcu_start() initialization with WARN_ON_ONCE()
  rcu: Remove redundant CONFIG_PROVE_RCU #if condition
  ...

Author: torvalds

.mailmap

@@ -467,7 +467,8 @@ Nadia Yvette Chambers <[email protected]> William Lee Irwin III <wli@holomorphy
 Naoya Horiguchi <[email protected]> <[email protected]>
 Naoya Horiguchi <[email protected]> <[email protected]>
 Nathan Chancellor <[email protected]> <[email protected]>
-Neeraj Upadhyay <[email protected]> <[email protected]>
+Neeraj Upadhyay <[email protected]> <[email protected]>
+Neeraj Upadhyay <[email protected]> <[email protected]>
 Neil Armstrong <[email protected]> <[email protected]>
 Nguyen Anh Quynh <[email protected]>
 Nicholas Piggin <[email protected]> <[email protected]>

Documentation/RCU/whatisRCU.rst

@@ -427,7 +427,7 @@ their assorted primitives.
 
 This section shows a simple use of the core RCU API to protect a
 global pointer to a dynamically allocated structure.  More-typical
-uses of RCU may be found in listRCU.rst, arrayRCU.rst, and NMI-RCU.rst.
+uses of RCU may be found in listRCU.rst and NMI-RCU.rst.
 ::
 
 	struct foo {
@@ -510,8 +510,8 @@ So, to sum up:
 	data item.
 
 See checklist.rst for additional rules to follow when using RCU.
-And again, more-typical uses of RCU may be found in listRCU.rst,
-arrayRCU.rst, and NMI-RCU.rst.
+And again, more-typical uses of RCU may be found in listRCU.rst
+and NMI-RCU.rst.
 
 .. _4_whatisRCU:
 

Documentation/admin-guide/kernel-parameters.txt

@@ -5098,6 +5098,20 @@
 			delay, memory pressure or callback list growing too
 			big.
 
+	rcutree.rcu_normal_wake_from_gp= [KNL]
+			Reduces a latency of synchronize_rcu() call. This approach
+			maintains its own track of synchronize_rcu() callers, so it
+			does not interact with regular callbacks because it does not
+			use a call_rcu[_hurry]() path. Please note, this is for a
+			normal grace period.
+
+			How to enable it:
+
+			echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp
+			or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1"
+
+			Default is 0.
+
 	rcuscale.gp_async= [KNL]
 			Measure performance of asynchronous
 			grace-period primitives such as call_rcu().

MAINTAINERS

@@ -18600,7 +18600,7 @@ F:	tools/testing/selftests/resctrl/
 READ-COPY UPDATE (RCU)
 M:	"Paul E. McKenney" <[email protected]>
 M:	Frederic Weisbecker <[email protected]> (kernel/rcu/tree_nocb.h)
-M:	Neeraj Upadhyay <[email protected]> (kernel/rcu/tasks.h)
+M:	Neeraj Upadhyay <[email protected]> (kernel/rcu/tasks.h)
 M:	Joel Fernandes <[email protected]>
 M:	Josh Triplett <[email protected]>
 M:	Boqun Feng <[email protected]>

arch/Kconfig

@@ -63,7 +63,7 @@ config KPROBES
 	depends on MODULES
 	depends on HAVE_KPROBES
 	select KALLSYMS
-	select TASKS_RCU if PREEMPTION
+	select NEED_TASKS_RCU
 	help
 	  Kprobes allows you to trap at almost any kernel address and
 	  execute a callback function.  register_kprobe() establishes
@@ -112,7 +112,7 @@ config STATIC_CALL_SELFTEST
 config OPTPROBES
 	def_bool y
 	depends on KPROBES && HAVE_OPTPROBES
-	select TASKS_RCU if PREEMPTION
+	select NEED_TASKS_RCU
 
 config KPROBES_ON_FTRACE
 	def_bool y

include/linux/rcupdate.h

@@ -401,15 +401,15 @@ static inline int debug_lockdep_rcu_enabled(void)
 		}							\
 	} while (0)
 
-#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
+#ifndef CONFIG_PREEMPT_RCU
 static inline void rcu_preempt_sleep_check(void)
 {
 	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
 			 "Illegal context switch in RCU read-side critical section");
 }
-#else /* #ifdef CONFIG_PROVE_RCU */
+#else // #ifndef CONFIG_PREEMPT_RCU
 static inline void rcu_preempt_sleep_check(void) { }
-#endif /* #else #ifdef CONFIG_PROVE_RCU */
+#endif // #else // #ifndef CONFIG_PREEMPT_RCU
 
 #define rcu_sleep_check()						\
 	do {								\
@@ -809,9 +809,9 @@ static inline void rcu_read_unlock(void)
 {
 	RCU_LOCKDEP_WARN(!rcu_is_watching(),
 			 "rcu_read_unlock() used illegally while idle");
+	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
 	__release(RCU);
 	__rcu_read_unlock();
-	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
 }
 
 /**
@@ -1090,6 +1090,18 @@ rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
 extern int rcu_expedited;
 extern int rcu_normal;
 
-DEFINE_LOCK_GUARD_0(rcu, rcu_read_lock(), rcu_read_unlock())
+DEFINE_LOCK_GUARD_0(rcu,
+	do {
+		rcu_read_lock();
+		/*
+		 * sparse doesn't call the cleanup function,
+		 * so just release immediately and don't track
+		 * the context. We don't need to anyway, since
+		 * the whole point of the guard is to not need
+		 * the explicit unlock.
+		 */
+		__release(RCU);
+	} while (0),
+	rcu_read_unlock())
 
 #endif /* __LINUX_RCUPDATE_H */

include/linux/rcupdate_wait.h

@@ -19,18 +19,18 @@ struct rcu_synchronize {
 };
 void wakeme_after_rcu(struct rcu_head *head);
 
-void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
+void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *crcu_array,
 		   struct rcu_synchronize *rs_array);
 
-#define _wait_rcu_gp(checktiny, ...) \
-do {									\
-	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };		\
-	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];	\
-	__wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array),		\
-			__crcu_array, __rs_array);			\
+#define _wait_rcu_gp(checktiny, state, ...) \
+do {												\
+	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };					\
+	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];				\
+	__wait_rcu_gp(checktiny, state, ARRAY_SIZE(__crcu_array), __crcu_array, __rs_array);	\
 } while (0)
 
-#define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
+#define wait_rcu_gp(...) _wait_rcu_gp(false, TASK_UNINTERRUPTIBLE, __VA_ARGS__)
+#define wait_rcu_gp_state(state, ...) _wait_rcu_gp(false, state, __VA_ARGS__)
 
 /**
  * synchronize_rcu_mult - Wait concurrently for multiple grace periods
@@ -54,7 +54,7 @@ do {									\
  * grace period.
  */
 #define synchronize_rcu_mult(...) \
-	_wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
+	_wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), TASK_UNINTERRUPTIBLE, __VA_ARGS__)
 
 static inline void cond_resched_rcu(void)
 {

include/linux/srcutiny.h

@@ -64,8 +64,10 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
 {
 	int idx;
 
+	preempt_disable();  // Needed for PREEMPT_AUTO
 	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
+	preempt_enable();
 	return idx;
 }
 

include/trace/events/rcu.h

@@ -707,6 +707,33 @@ TRACE_EVENT_RCU(rcu_invoke_kfree_bulk_callback,
 		__entry->rcuname, __entry->p, __entry->nr_records)
 );
 
+/*
+ * Tracepoint for a normal synchronize_rcu() states. The first argument
+ * is the RCU flavor, the second argument is a pointer to rcu_head the
+ * last one is an event.
+ */
+TRACE_EVENT_RCU(rcu_sr_normal,
+
+	TP_PROTO(const char *rcuname, struct rcu_head *rhp, const char *srevent),
+
+	TP_ARGS(rcuname, rhp, srevent),
+
+	TP_STRUCT__entry(
+		__field(const char *, rcuname)
+		__field(void *, rhp)
+		__field(const char *, srevent)
+	),
+
+	TP_fast_assign(
+		__entry->rcuname = rcuname;
+		__entry->rhp = rhp;
+		__entry->srevent = srevent;
+	),
+
+	TP_printk("%s rhp=0x%p event=%s",
+		__entry->rcuname, __entry->rhp, __entry->srevent)
+);
+
 /*
  * Tracepoint for exiting rcu_do_batch after RCU callbacks have been
  * invoked.  The first argument is the name of the RCU flavor,

kernel/bpf/Kconfig

@@ -28,7 +28,7 @@ config BPF_SYSCALL
 	bool "Enable bpf() system call"
 	select BPF
 	select IRQ_WORK
-	select TASKS_RCU if PREEMPTION
+	select NEED_TASKS_RCU
 	select TASKS_TRACE_RCU
 	select BINARY_PRINTF
 	select NET_SOCK_MSG if NET