Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney: - Miscellaneous fixes. (Paul E. McKenney, Boqun Feng, Oleg Nesterov, Patrick Marlier) - Improvements to expedited grace periods. (Paul E. McKenney) - Performance improvements to and locktorture tests for percpu-rwsem. (Oleg Nesterov, Paul E. McKenney) - Torture-test changes. (Paul E. McKenney, Davidlohr Bueso) - Documentation updates. (Paul E. McKenney) Signed-off-by: Ingo Molnar <mingo@kernel.org>
2026-05-01 15:00:59 -07:00 · 2015-10-19 10:09:54 +02:00
parent 7379047d55 39cd2dd39a
commit c13dc31adb
41 changed files with 1331 additions and 543 deletions
@@ -205,6 +205,13 @@ o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the
 	behavior, you might need to replace some of the cond_resched()
 	calls with calls to cond_resched_rcu_qs().

+o	Booting Linux using a console connection that is too slow to
+	keep up with the boot-time console-message rate.  For example,
+	a 115Kbaud serial console can be -way- too slow to keep up
+	with boot-time message rates, and will frequently result in
+	RCU CPU stall warning messages.  Especially if you have added
+	debug printk()s.
+
 o	Anything that prevents RCU's grace-period kthreads from running.
 	This can result in the "All QSes seen" console-log message.
 	This message will include information on when the kthread last
@@ -166,40 +166,27 @@ test_no_idle_hz	Whether or not to test the ability of RCU to operate in

 torture_type	The type of RCU to test, with string values as follows:

-		"rcu":  rcu_read_lock(), rcu_read_unlock() and call_rcu().
-
-		"rcu_sync":  rcu_read_lock(), rcu_read_unlock(), and
-			synchronize_rcu().
-
-		"rcu_expedited": rcu_read_lock(), rcu_read_unlock(), and
-			synchronize_rcu_expedited().
+		"rcu":  rcu_read_lock(), rcu_read_unlock() and call_rcu(),
+			along with expedited, synchronous, and polling
+			variants.

 		"rcu_bh": rcu_read_lock_bh(), rcu_read_unlock_bh(), and
-			call_rcu_bh().
+			call_rcu_bh(), along with expedited and synchronous
+			variants.

-		"rcu_bh_sync": rcu_read_lock_bh(), rcu_read_unlock_bh(),
-			and synchronize_rcu_bh().
-
-		"rcu_bh_expedited": rcu_read_lock_bh(), rcu_read_unlock_bh(),
-			and synchronize_rcu_bh_expedited().
+		"rcu_busted": This tests an intentionally incorrect version
+			of RCU in order to help test rcutorture itself.

 		"srcu": srcu_read_lock(), srcu_read_unlock() and
-			call_srcu().
-
-		"srcu_sync": srcu_read_lock(), srcu_read_unlock() and
-			synchronize_srcu().
-
-		"srcu_expedited": srcu_read_lock(), srcu_read_unlock() and
-			synchronize_srcu_expedited().
+			call_srcu(), along with expedited and
+			synchronous variants.

 		"sched": preempt_disable(), preempt_enable(), and
-			call_rcu_sched().
+			call_rcu_sched(), along with expedited,
+			synchronous, and polling variants.

-		"sched_sync": preempt_disable(), preempt_enable(), and
-			synchronize_sched().
-
-		"sched_expedited": preempt_disable(), preempt_enable(), and
-			synchronize_sched_expedited().
+		"tasks": voluntary context switch and call_rcu_tasks(),
+			along with expedited and synchronous variants.

 		Defaults to "rcu".

@@ -56,14 +56,14 @@ rcuboost:

 The output of "cat rcu/rcu_preempt/rcudata" looks as follows:

-  0!c=30455 g=30456 pq=1/0 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716
-  1!c=30719 g=30720 pq=1/0 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982
-  2!c=30150 g=30151 pq=1/1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458
-  3 c=31249 g=31250 pq=1/1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622
-  4!c=29502 g=29503 pq=1/0 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521
-  5 c=31201 g=31202 pq=1/0 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698
-  6!c=30253 g=30254 pq=1/0 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353
-  7 c=31178 g=31178 pq=1/0 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969
+  0!c=30455 g=30456 cnq=1/0:1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716
+  1!c=30719 g=30720 cnq=1/0:0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982
+  2!c=30150 g=30151 cnq=1/1:1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458
+  3 c=31249 g=31250 cnq=1/1:0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622
+  4!c=29502 g=29503 cnq=1/0:1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521
+  5 c=31201 g=31202 cnq=1/0:1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698
+  6!c=30253 g=30254 cnq=1/0:1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353
+  7 c=31178 g=31178 cnq=1/0:0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969

 This file has one line per CPU, or eight for this 8-CPU system.
 The fields are as follows:
@@ -188,14 +188,14 @@ o	"ca" is the number of RCU callbacks that have been adopted by this
 Kernels compiled with CONFIG_RCU_BOOST=y display the following from
 /debug/rcu/rcu_preempt/rcudata:

-  0!c=12865 g=12866 pq=1/0 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871
-  1 c=14407 g=14408 pq=1/0 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485
-  2 c=14407 g=14408 pq=1/0 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490
-  3 c=14407 g=14408 pq=1/0 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290
-  4 c=14405 g=14406 pq=1/0 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114
-  5!c=14168 g=14169 pq=1/0 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722
-  6 c=14404 g=14405 pq=1/0 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811
-  7 c=14407 g=14408 pq=1/0 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042
+  0!c=12865 g=12866 cnq=1/0:1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871
+  1 c=14407 g=14408 cnq=1/0:0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485
+  2 c=14407 g=14408 cnq=1/0:0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490
+  3 c=14407 g=14408 cnq=1/0:0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290
+  4 c=14405 g=14406 cnq=1/0:1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114
+  5!c=14168 g=14169 cnq=1/0:0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722
+  6 c=14404 g=14405 cnq=1/0:0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811
+  7 c=14407 g=14408 cnq=1/0:1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042

 This is similar to the output discussed above, but contains the following
 additional fields:
@@ -364,7 +364,7 @@ uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt.
 	};
 	DEFINE_SPINLOCK(foo_mutex);

-	struct foo *gbl_foo;
+	struct foo __rcu *gbl_foo;

 	/*
 	 * Create a new struct foo that is the same as the one currently
@@ -386,7 +386,7 @@ uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt.

 		new_fp = kmalloc(sizeof(*new_fp), GFP_KERNEL);
 		spin_lock(&foo_mutex);
-		old_fp = gbl_foo;
+		old_fp = rcu_dereference_protected(gbl_foo, lockdep_is_held(&foo_mutex));
 		*new_fp = *old_fp;
 		new_fp->a = new_a;
 		rcu_assign_pointer(gbl_foo, new_fp);
@@ -487,7 +487,7 @@ The foo_update_a() function might then be written as follows:

 		new_fp = kmalloc(sizeof(*new_fp), GFP_KERNEL);
 		spin_lock(&foo_mutex);
-		old_fp = gbl_foo;
+		old_fp = rcu_dereference_protected(gbl_foo, lockdep_is_held(&foo_mutex));
 		*new_fp = *old_fp;
 		new_fp->a = new_a;
 		rcu_assign_pointer(gbl_foo, new_fp);
@@ -3074,9 +3074,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			cache-to-cache transfer latencies.

 	rcutree.rcu_fanout_leaf= [KNL]
-			Increase the number of CPUs assigned to each
-			leaf rcu_node structure.  Useful for very large
-			systems.
+			Change the number of CPUs assigned to each
+			leaf rcu_node structure.  Useful for very
+			large systems, which will choose the value 64,
+			and for NUMA systems with large remote-access
+			latencies, which will choose a value aligned
+			with the appropriate hardware boundaries.

 	rcutree.jiffies_till_sched_qs= [KNL]
 			Set required age in jiffies for a
@@ -52,6 +52,9 @@ torture_type	  Type of lock to torture. By default, only spinlocks will

 		     o "mutex_lock": mutex_lock() and mutex_unlock() pairs.

+		     o "rtmutex_lock": rtmutex_lock() and rtmutex_unlock()
+				       pairs. Kernel must have CONFIG_RT_MUTEX=y.
+
 		     o "rwsem_lock": read/write down() and up() semaphore pairs.

 torture_runnable  Start locktorture at boot time in the case where the
@@ -1710,6 +1710,17 @@ There are some more advanced barrier functions:
     operations" subsection for information on where to use these.


+ (*) lockless_dereference();
+     This can be thought of as a pointer-fetch wrapper around the
+     smp_read_barrier_depends() data-dependency barrier.
+
+     This is also similar to rcu_dereference(), but in cases where
+     object lifetime is handled by some mechanism other than RCU, for
+     example, when the objects removed only when the system goes down.
+     In addition, lockless_dereference() is used in some data structures
+     that can be used both with and without RCU.
+
+
 (*) dma_wmb();
 (*) dma_rmb();

@@ -1789,7 +1800,6 @@ The Linux kernel has a number of locking constructs:
 (*) mutexes
 (*) semaphores
 (*) R/W semaphores
- (*) RCU

 In all cases there are variants on "ACQUIRE" operations and "RELEASE" operations
 for each construct.  These operations all imply certain barriers:
@@ -228,7 +228,6 @@ extern struct bus_type cpu_subsys;
 extern void cpu_hotplug_begin(void);
 extern void cpu_hotplug_done(void);
 extern void get_online_cpus(void);
-extern bool try_get_online_cpus(void);
 extern void put_online_cpus(void);
 extern void cpu_hotplug_disable(void);
 extern void cpu_hotplug_enable(void);
@@ -246,7 +245,6 @@ int cpu_down(unsigned int cpu);
 static inline void cpu_hotplug_begin(void) {}
 static inline void cpu_hotplug_done(void) {}
 #define get_online_cpus()	do { } while (0)
-#define try_get_online_cpus()	true
 #define put_online_cpus()	do { } while (0)
 #define cpu_hotplug_disable()	do { } while (0)
 #define cpu_hotplug_enable()	do { } while (0)
@@ -87,7 +87,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head)
 static inline void __list_del(struct list_head * prev, struct list_head * next)
 {
 	next->prev = prev;
-	prev->next = next;
+	WRITE_ONCE(prev->next, next);
 }

 /**
@@ -615,7 +615,8 @@ static inline void __hlist_del(struct hlist_node *n)
 {
 	struct hlist_node *next = n->next;
 	struct hlist_node **pprev = n->pprev;
-	*pprev = next;
+
+	WRITE_ONCE(*pprev, next);
 	if (next)
 		next->pprev = pprev;
 }
@@ -93,9 +93,10 @@ static inline void __hlist_bl_del(struct hlist_bl_node *n)
 	LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);

 	/* pprev may be `first`, so be careful not to lose the lock bit */
-	*pprev = (struct hlist_bl_node *)
+	WRITE_ONCE(*pprev,
+		   (struct hlist_bl_node *)
 			((unsigned long)next |
-			 ((unsigned long)*pprev & LIST_BL_LOCKMASK));
+			 ((unsigned long)*pprev & LIST_BL_LOCKMASK)));
 	if (next)
 		next->pprev = pprev;
 }
@@ -76,7 +76,8 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
 {
 	struct hlist_nulls_node *next = n->next;
 	struct hlist_nulls_node **pprev = n->pprev;
-	*pprev = next;
+
+	WRITE_ONCE(*pprev, next);
 	if (!is_a_nulls(next))
 		next->pprev = pprev;
 }
@@ -5,11 +5,12 @@
 #include <linux/rwsem.h>
 #include <linux/percpu.h>
 #include <linux/wait.h>
+#include <linux/rcu_sync.h>
 #include <linux/lockdep.h>

 struct percpu_rw_semaphore {
+	struct rcu_sync		rss;
 	unsigned int __percpu	*fast_read_ctr;
-	atomic_t		write_ctr;
 	struct rw_semaphore	rw_sem;
 	atomic_t		slow_read_ctr;
 	wait_queue_head_t	write_waitq;
@@ -0,0 +1,86 @@
+/*
+ * RCU-based infrastructure for lightweight reader-writer locking
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (c) 2015, Red Hat, Inc.
+ *
+ * Author: Oleg Nesterov <oleg@redhat.com>
+ */
+
+#ifndef _LINUX_RCU_SYNC_H_
+#define _LINUX_RCU_SYNC_H_
+
+#include <linux/wait.h>
+#include <linux/rcupdate.h>
+
+enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
+
+/* Structure to mediate between updaters and fastpath-using readers.  */
+struct rcu_sync {
+	int			gp_state;
+	int			gp_count;
+	wait_queue_head_t	gp_wait;
+
+	int			cb_state;
+	struct rcu_head		cb_head;
+
+	enum rcu_sync_type	gp_type;
+};
+
+extern void rcu_sync_lockdep_assert(struct rcu_sync *);
+
+/**
+ * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
+ * @rsp: Pointer to rcu_sync structure to use for synchronization
+ *
+ * Returns true if readers are permitted to use their fastpaths.
+ * Must be invoked within an RCU read-side critical section whose
+ * flavor matches that of the rcu_sync struture.
+ */
+static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
+{
+#ifdef CONFIG_PROVE_RCU
+	rcu_sync_lockdep_assert(rsp);
+#endif
+	return !rsp->gp_state; /* GP_IDLE */
+}
+
+extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_enter(struct rcu_sync *);
+extern void rcu_sync_exit(struct rcu_sync *);
+extern void rcu_sync_dtor(struct rcu_sync *);
+
+#define __RCU_SYNC_INITIALIZER(name, type) {				\
+		.gp_state = 0,						\
+		.gp_count = 0,						\
+		.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),	\
+		.cb_state = 0,						\
+		.gp_type = type,					\
+	}
+
+#define	__DEFINE_RCU_SYNC(name, type)	\
+	struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
+
+#define DEFINE_RCU_SYNC(name)		\
+	__DEFINE_RCU_SYNC(name, RCU_SYNC)
+
+#define DEFINE_RCU_SCHED_SYNC(name)	\
+	__DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
+
+#define DEFINE_RCU_BH_SYNC(name)	\
+	__DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
+
+#endif /* _LINUX_RCU_SYNC_H_ */
@@ -247,10 +247,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
 */
 #define list_entry_rcu(ptr, type, member) \
-({ \
-	typeof(*ptr) __rcu *__ptr = (typeof(*ptr) __rcu __force *)ptr; \
-	container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
-})
+	container_of(lockless_dereference(ptr), type, member)

 /**
 * Where are list_empty_rcu() and list_first_entry_rcu()?
@@ -160,7 +160,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 * more than one CPU).
 */
 void call_rcu(struct rcu_head *head,
-	      void (*func)(struct rcu_head *head));
+	      rcu_callback_t func);

 #else /* #ifdef CONFIG_PREEMPT_RCU */

@@ -191,7 +191,7 @@ void call_rcu(struct rcu_head *head,
 * memory ordering guarantees.
 */
 void call_rcu_bh(struct rcu_head *head,
-		 void (*func)(struct rcu_head *head));
+		 rcu_callback_t func);

 /**
 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
@@ -213,7 +213,7 @@ void call_rcu_bh(struct rcu_head *head,
 * memory ordering guarantees.
 */
 void call_rcu_sched(struct rcu_head *head,
-		    void (*func)(struct rcu_head *rcu));
+		    rcu_callback_t func);

 void synchronize_sched(void);

@@ -274,7 +274,7 @@ do {									\
 * See the description of call_rcu() for more detailed information on
 * memory ordering guarantees.
 */
-void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head));
+void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
 void synchronize_rcu_tasks(void);
 void rcu_barrier_tasks(void);

@@ -297,12 +297,14 @@ void synchronize_rcu(void);

 static inline void __rcu_read_lock(void)
 {
-	preempt_disable();
+	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		preempt_disable();
 }

 static inline void __rcu_read_unlock(void)
 {
-	preempt_enable();
+	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		preempt_enable();
 }

 static inline void synchronize_rcu(void)
@@ -535,28 +537,8 @@ static inline int rcu_read_lock_sched_held(void)

 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

-/* Deprecate rcu_lockdep_assert():  Use RCU_LOCKDEP_WARN() instead. */
-static inline void __attribute((deprecated)) deprecate_rcu_lockdep_assert(void)
-{
-}
-
 #ifdef CONFIG_PROVE_RCU

-/**
- * rcu_lockdep_assert - emit lockdep splat if specified condition not met
- * @c: condition to check
- * @s: informative message
- */
-#define rcu_lockdep_assert(c, s)					\
-	do {								\
-		static bool __section(.data.unlikely) __warned;		\
-		deprecate_rcu_lockdep_assert();				\
-		if (debug_lockdep_rcu_enabled() && !__warned && !(c)) {	\
-			__warned = true;				\
-			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
-		}							\
-	} while (0)
-
 /**
 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
 * @c: condition to check
@@ -594,7 +576,6 @@ static inline void rcu_preempt_sleep_check(void)

 #else /* #ifdef CONFIG_PROVE_RCU */

-#define rcu_lockdep_assert(c, s) deprecate_rcu_lockdep_assert()
 #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
 #define rcu_sleep_check() do { } while (0)

@@ -810,6 +791,28 @@ static inline void rcu_preempt_sleep_check(void)
 */
 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)

+/**
+ * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
+ * @p: The pointer to hand off
+ *
+ * This is simply an identity function, but it documents where a pointer
+ * is handed off from RCU to some other synchronization mechanism, for
+ * example, reference counting or locking.  In C11, it would map to
+ * kill_dependency().  It could be used as follows:
+ *
+ *	rcu_read_lock();
+ *	p = rcu_dereference(gp);
+ *	long_lived = is_long_lived(p);
+ *	if (long_lived) {
+ *		if (!atomic_inc_not_zero(p->refcnt))
+ *			long_lived = false;
+ *		else
+ *			p = rcu_pointer_handoff(p);
+ *	}
+ *	rcu_read_unlock();
+ */
+#define rcu_pointer_handoff(p) (p)
+
 /**
 * rcu_read_lock() - mark the beginning of an RCU read-side critical section
 *
@@ -1065,7 +1068,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define __kfree_rcu(head, offset) \
 	do { \
 		BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
-		kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
+		kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
 	} while (0)

 /**
@@ -83,7 +83,7 @@ static inline void synchronize_sched_expedited(void)
 }

 static inline void kfree_call_rcu(struct rcu_head *head,
-				  void (*func)(struct rcu_head *rcu))
+				  rcu_callback_t func)
 {
 	call_rcu(head, func);
 }
@@ -216,6 +216,7 @@ static inline bool rcu_is_watching(void)

 static inline void rcu_all_qs(void)
 {
+	barrier(); /* Avoid RCU read-side critical sections leaking across. */
 }

 #endif /* __LINUX_RCUTINY_H */
@@ -48,7 +48,7 @@ void synchronize_rcu_bh(void);
 void synchronize_sched_expedited(void);
 void synchronize_rcu_expedited(void);

-void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func);

 /**
 * synchronize_rcu_bh_expedited - Brute-force RCU-bh grace period
@@ -1342,10 +1342,12 @@ struct sched_dl_entity {

 union rcu_special {
 	struct {
-		bool blocked;
-		bool need_qs;
-	} b;
-	short s;
+		u8 blocked;
+		u8 need_qs;
+		u8 exp_need_qs;
+		u8 pad;	/* Otherwise the compiler can store garbage here. */
+	} b; /* Bits. */
+	u32 s; /* Set of bits. */
 };
 struct rcu_node;

@@ -215,8 +215,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
 */
 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 {
-	int retval = __srcu_read_lock(sp);
+	int retval;

+	preempt_disable();
+	retval = __srcu_read_lock(sp);
+	preempt_enable();
 	rcu_lock_acquire(&(sp)->dep_map);
 	return retval;
 }
@@ -102,19 +102,6 @@ void get_online_cpus(void)
 }
 EXPORT_SYMBOL_GPL(get_online_cpus);

-bool try_get_online_cpus(void)
-{
-	if (cpu_hotplug.active_writer == current)
-		return true;
-	if (!mutex_trylock(&cpu_hotplug.lock))
-		return false;
-	cpuhp_lock_acquire_tryread();
-	atomic_inc(&cpu_hotplug.refcount);
-	mutex_unlock(&cpu_hotplug.lock);
-	return true;
-}
-EXPORT_SYMBOL_GPL(try_get_online_cpus);
-
 void put_online_cpus(void)
 {
 	int refcount;
--- a/Show More
+++ b/Show More