Merge branches 'doc.2021.01.06a', 'fixes.2021.01.04b', 'kfree_rcu.202…

…1.01.04a', 'mmdumpobj.2021.01.22a', 'nocb.2021.01.06a', 'rt.2021.01.04a', 'stall.2021.01.06a', 'torture.2021.01.12a' and 'tortureall.2021.01.06a' into HEAD

doc.2021.01.06a: Documentation updates.
fixes.2021.01.04b: Miscellaneous fixes.
kfree_rcu.2021.01.04a: kfree_rcu() updates.
mmdumpobj.2021.01.22a: Dump allocation point for memory blocks.
nocb.2021.01.06a: RCU callback offload updates and cblist segment lengths.
rt.2021.01.04a: Real-time updates.
stall.2021.01.06a: RCU CPU stall warning updates.
torture.2021.01.12a: Torture-test updates and polling SRCU grace-period API.
tortureall.2021.01.06a: Torture-test script updates.

Documentation/RCU/Design/Requirements/Requirements.rst

@@ -2598,6 +2598,24 @@ also includes DEFINE_SRCU(), DEFINE_STATIC_SRCU(), and
 init_srcu_struct() APIs for defining and initializing
 ``srcu_struct`` structures.
 
+More recently, the SRCU API has added polling interfaces:
+
+#. start_poll_synchronize_srcu() returns a cookie identifying
+   the completion of a future SRCU grace period and ensures
+   that this grace period will be started.
+#. poll_state_synchronize_srcu() returns ``true`` iff the
+   specified cookie corresponds to an already-completed
+   SRCU grace period.
+#. get_state_synchronize_srcu() returns a cookie just like
+   start_poll_synchronize_srcu() does, but differs in that
+   it does nothing to ensure that any future SRCU grace period
+   will be started.
+
+These functions are used to avoid unnecessary SRCU grace periods in
+certain types of buffer-cache algorithms having multi-stage age-out
+mechanisms.  The idea is that by the time the block has aged completely
+from the cache, an SRCU grace period will be very likely to have elapsed.
+
 Tasks RCU
 ~~~~~~~~~
 

Documentation/RCU/stallwarn.rst

@@ -92,7 +92,9 @@ warnings:
 	buggy timer hardware through bugs in the interrupt or exception
 	path (whether hardware, firmware, or software) through bugs
 	in Linux's timer subsystem through bugs in the scheduler, and,
-	yes, even including bugs in RCU itself.
+	yes, even including bugs in RCU itself.  It can also result in
+	the ``rcu_.*timer wakeup didn't happen for`` console-log message,
+	which will include additional debugging information.
 
 -	A bug in the RCU implementation.
 
@@ -292,6 +294,25 @@ kthread is waiting for a short timeout, the "state" precedes value of the
 task_struct ->state field, and the "cpu" indicates that the grace-period
 kthread last ran on CPU 5.
 
+If the relevant grace-period kthread does not wake from FQS wait in a
+reasonable time, then the following additional line is printed::
+
+	kthread timer wakeup didn't happen for 23804 jiffies! g7076 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
+
+The "23804" indicates that kthread's timer expired more than 23 thousand
+jiffies ago.  The rest of the line has meaning similar to the kthread
+starvation case.
+
+Additionally, the following line is printed::
+
+	Possible timer handling issue on cpu=4 timer-softirq=11142
+
+Here "cpu" indicates that the grace-period kthread last ran on CPU 4,
+where it queued the fqs timer.  The number following the "timer-softirq"
+is the current ``TIMER_SOFTIRQ`` count on cpu 4.  If this value does not
+change on successive RCU CPU stall warnings, there is further reason to
+suspect a timer problem.
+
 
 Multiple Warnings From One Stall
 ================================

Documentation/admin-guide/kernel-parameters.txt

@@ -4092,6 +4092,10 @@
 			value, meaning that RCU_SOFTIRQ is used by default.
 			Specify rcutree.use_softirq=0 to use rcuc kthreads.
 
+			But note that CONFIG_PREEMPT_RT=y kernels disable
+			this kernel boot parameter, forcibly setting it
+			to zero.
+
 	rcutree.rcu_fanout_exact= [KNL]
 			Disable autobalancing of the rcu_node combining
 			tree.  This is used by rcutorture, and might
@@ -4332,6 +4336,14 @@
 			stress RCU, they don't participate in the actual
 			test, hence the "fake".
 
+	rcutorture.nocbs_nthreads= [KNL]
+			Set number of RCU callback-offload togglers.
+			Zero (the default) disables toggling.
+
+	rcutorture.nocbs_toggle= [KNL]
+			Set the delay in milliseconds between successive
+			callback-offload toggling attempts.
+
 	rcutorture.nreaders= [KNL]
 			Set number of RCU readers.  The value -1 selects
 			N-1, where N is the number of CPUs.  A value
@@ -4464,6 +4476,13 @@
 			only normal grace-period primitives.  No effect
 			on CONFIG_TINY_RCU kernels.
 
+			But note that CONFIG_PREEMPT_RT=y kernels enables
+			this kernel boot parameter, forcibly setting
+			it to the value one, that is, converting any
+			post-boot attempt at an expedited RCU grace
+			period to instead use normal non-expedited
+			grace-period processing.
+
 	rcupdate.rcu_task_ipi_delay= [KNL]
 			Set time in jiffies during which RCU tasks will
 			avoid sending IPIs, starting with the beginning
@@ -4551,6 +4570,12 @@
 	refscale.verbose= [KNL]
 			Enable additional printk() statements.
 
+	refscale.verbose_batched= [KNL]
+			Batch the additional printk() statements.  If zero
+			(the default) or negative, print everything.  Otherwise,
+			print every Nth verbose statement, where N is the value
+			specified.
+
 	relax_domain_level=
 			[KNL, SMP] Set scheduler's default relax_domain_level.
 			See Documentation/admin-guide/cgroup-v1/cpusets.rst.
@@ -5325,6 +5350,14 @@
 			are running concurrently, especially on systems
 			with rotating-rust storage.
 
+	torture.verbose_sleep_frequency= [KNL]
+			Specifies how many verbose printk()s should be
+			emitted between each sleep.  The default of zero
+			disables verbose-printk() sleeping.
+
+	torture.verbose_sleep_duration= [KNL]
+			Duration of each verbose-printk() sleep in jiffies.
+
 	tp720=		[HW,PS2]
 
 	tpm_suspend_pcr=[HW,TPM]

include/linux/cpu.h

@@ -111,6 +111,8 @@ static inline void cpu_maps_update_done(void)
 #endif /* CONFIG_SMP */
 extern struct bus_type cpu_subsys;
 
+extern int lockdep_is_cpus_held(void);
+
 #ifdef CONFIG_HOTPLUG_CPU
 extern void cpus_write_lock(void);
 extern void cpus_write_unlock(void);

include/linux/mm.h

@@ -3169,5 +3169,7 @@ unsigned long wp_shared_mapping_range(struct address_space *mapping,
 
 extern int sysctl_nr_trim_pages;
 
+void mem_dump_obj(void *object);
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */

include/linux/rcu_segcblist.h

@@ -63,6 +63,122 @@ struct rcu_cblist {
 #define RCU_NEXT_TAIL		3
 #define RCU_CBLIST_NSEGS	4
 
+
+/*
+ *                     ==NOCB Offloading state machine==
+ *
+ *
+ *  ----------------------------------------------------------------------------
+ *  |                         SEGCBLIST_SOFTIRQ_ONLY                           |
+ *  |                                                                          |
+ *  |  Callbacks processed by rcu_core() from softirqs or local                |
+ *  |  rcuc kthread, without holding nocb_lock.                                |
+ *  ----------------------------------------------------------------------------
+ *                                         |
+ *                                         v
+ *  ----------------------------------------------------------------------------
+ *  |                        SEGCBLIST_OFFLOADED                               |
+ *  |                                                                          |
+ *  | Callbacks processed by rcu_core() from softirqs or local                 |
+ *  | rcuc kthread, while holding nocb_lock. Waking up CB and GP kthreads,     |
+ *  | allowing nocb_timer to be armed.                                         |
+ *  ----------------------------------------------------------------------------
+ *                                         |
+ *                                         v
+ *                        -----------------------------------
+ *                        |                                 |
+ *                        v                                 v
+ *  ---------------------------------------  ----------------------------------|
+ *  |        SEGCBLIST_OFFLOADED |        |  |     SEGCBLIST_OFFLOADED |       |
+ *  |        SEGCBLIST_KTHREAD_CB         |  |     SEGCBLIST_KTHREAD_GP        |
+ *  |                                     |  |                                 |
+ *  |                                     |  |                                 |
+ *  | CB kthread woke up and              |  | GP kthread woke up and          |
+ *  | acknowledged SEGCBLIST_OFFLOADED.   |  | acknowledged SEGCBLIST_OFFLOADED|
+ *  | Processes callbacks concurrently    |  |                                 |
+ *  | with rcu_core(), holding            |  |                                 |
+ *  | nocb_lock.                          |  |                                 |
+ *  ---------------------------------------  -----------------------------------
+ *                        |                                 |
+ *                        -----------------------------------
+ *                                         |
+ *                                         v
+ *  |--------------------------------------------------------------------------|
+ *  |                           SEGCBLIST_OFFLOADED |                          |
+ *  |                           SEGCBLIST_KTHREAD_CB |                         |
+ *  |                           SEGCBLIST_KTHREAD_GP                           |
+ *  |                                                                          |
+ *  |   Kthreads handle callbacks holding nocb_lock, local rcu_core() stops    |
+ *  |   handling callbacks.                                                    |
+ *  ----------------------------------------------------------------------------
+ */
+
+
+
+/*
+ *                       ==NOCB De-Offloading state machine==
+ *
+ *
+ *  |--------------------------------------------------------------------------|
+ *  |                           SEGCBLIST_OFFLOADED |                          |
+ *  |                           SEGCBLIST_KTHREAD_CB |                         |
+ *  |                           SEGCBLIST_KTHREAD_GP                           |
+ *  |                                                                          |
+ *  |   CB/GP kthreads handle callbacks holding nocb_lock, local rcu_core()    |
+ *  |   ignores callbacks.                                                     |
+ *  ----------------------------------------------------------------------------
+ *                                      |
+ *                                      v
+ *  |--------------------------------------------------------------------------|
+ *  |                           SEGCBLIST_KTHREAD_CB |                         |
+ *  |                           SEGCBLIST_KTHREAD_GP                           |
+ *  |                                                                          |
+ *  |   CB/GP kthreads and local rcu_core() handle callbacks concurrently      |
+ *  |   holding nocb_lock. Wake up CB and GP kthreads if necessary.            |
+ *  ----------------------------------------------------------------------------
+ *                                      |
+ *                                      v
+ *                     -----------------------------------
+ *                     |                                 |
+ *                     v                                 v
+ *  ---------------------------------------------------------------------------|
+ *  |                                                                          |
+ *  |        SEGCBLIST_KTHREAD_CB         |       SEGCBLIST_KTHREAD_GP         |
+ *  |                                     |                                    |
+ *  | GP kthread woke up and              |   CB kthread woke up and           |
+ *  | acknowledged the fact that          |   acknowledged the fact that       |
+ *  | SEGCBLIST_OFFLOADED got cleared.    |   SEGCBLIST_OFFLOADED got cleared. |
+ *  |                                     |   The CB kthread goes to sleep     |
+ *  | The callbacks from the target CPU   |   until it ever gets re-offloaded. |
+ *  | will be ignored from the GP kthread |                                    |
+ *  | loop.                               |                                    |
+ *  ----------------------------------------------------------------------------
+ *                      |                                 |
+ *                      -----------------------------------
+ *                                      |
+ *                                      v
+ *  ----------------------------------------------------------------------------
+ *  |                                   0                                      |
+ *  |                                                                          |
+ *  | Callbacks processed by rcu_core() from softirqs or local                 |
+ *  | rcuc kthread, while holding nocb_lock. Forbid nocb_timer to be armed.    |
+ *  | Flush pending nocb_timer. Flush nocb bypass callbacks.                   |
+ *  ----------------------------------------------------------------------------
+ *                                      |
+ *                                      v
+ *  ----------------------------------------------------------------------------
+ *  |                         SEGCBLIST_SOFTIRQ_ONLY                           |
+ *  |                                                                          |
+ *  |  Callbacks processed by rcu_core() from softirqs or local                |
+ *  |  rcuc kthread, without holding nocb_lock.                                |
+ *  ----------------------------------------------------------------------------
+ */
+#define SEGCBLIST_ENABLED	BIT(0)
+#define SEGCBLIST_SOFTIRQ_ONLY	BIT(1)
+#define SEGCBLIST_KTHREAD_CB	BIT(2)
+#define SEGCBLIST_KTHREAD_GP	BIT(3)
+#define SEGCBLIST_OFFLOADED	BIT(4)
+
 struct rcu_segcblist {
 	struct rcu_head *head;
 	struct rcu_head **tails[RCU_CBLIST_NSEGS];
@@ -72,8 +188,8 @@ struct rcu_segcblist {
 #else
 	long len;
 #endif
-	u8 enabled;
-	u8 offloaded;
+	long seglen[RCU_CBLIST_NSEGS];
+	u8 flags;
 };
 
 #define RCU_SEGCBLIST_INITIALIZER(n) \

include/linux/rcupdate.h

@@ -33,6 +33,8 @@
 #define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
 #define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
 #define ulong2long(a)		(*(long *)(&(a)))
+#define USHORT_CMP_GE(a, b)	(USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
+#define USHORT_CMP_LT(a, b)	(USHRT_MAX / 2 < (unsigned short)((a) - (b)))
 
 /* Exported common interfaces */
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
@@ -86,6 +88,12 @@ void rcu_sched_clock_irq(int user);
 void rcu_report_dead(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);
 
+#ifdef CONFIG_TASKS_RCU_GENERIC
+void rcu_init_tasks_generic(void);
+#else
+static inline void rcu_init_tasks_generic(void) { }
+#endif
+
 #ifdef CONFIG_RCU_STALL_COMMON
 void rcu_sysrq_start(void);
 void rcu_sysrq_end(void);
@@ -104,8 +112,12 @@ static inline void rcu_user_exit(void) { }
 
 #ifdef CONFIG_RCU_NOCB_CPU
 void rcu_init_nohz(void);
+int rcu_nocb_cpu_offload(int cpu);
+int rcu_nocb_cpu_deoffload(int cpu);
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 static inline void rcu_init_nohz(void) { }
+static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
+static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 
 /**
@@ -840,19 +852,11 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  */
 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
 
-/*
- * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
- */
-#define __kvfree_rcu(head, offset) \
-	do { \
-		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offset)); \
-		kvfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
-	} while (0)
-
 /**
  * kfree_rcu() - kfree an object after a grace period.
- * @ptr:	pointer to kfree
- * @rhf:	the name of the struct rcu_head within the type of @ptr.
+ * @ptr: pointer to kfree for both single- and double-argument invocations.
+ * @rhf: the name of the struct rcu_head within the type of @ptr,
+ *       but only for double-argument invocations.
  *
  * Many rcu callbacks functions just call kfree() on the base structure.
  * These functions are trivial, but their size adds up, and furthermore
@@ -865,7 +869,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * Because the functions are not allowed in the low-order 4096 bytes of
  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
  * If the offset is larger than 4095 bytes, a compile-time error will
- * be generated in __kvfree_rcu(). If this error is triggered, you can
+ * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
  * either fall back to use of call_rcu() or rearrange the structure to
  * position the rcu_head structure into the first 4096 bytes.
  *
@@ -875,13 +879,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.
  */
-#define kfree_rcu(ptr, rhf)						\
-do {									\
-	typeof (ptr) ___p = (ptr);					\
-									\
-	if (___p)							\
-		__kvfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
-} while (0)
+#define kfree_rcu kvfree_rcu
 
 /**
  * kvfree_rcu() - kvfree an object after a grace period.
@@ -913,7 +911,17 @@ do {									\
 	kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
 
 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
-#define kvfree_rcu_arg_2(ptr, rhf) kfree_rcu(ptr, rhf)
+#define kvfree_rcu_arg_2(ptr, rhf)					\
+do {									\
+	typeof (ptr) ___p = (ptr);					\
+									\
+	if (___p) {									\
+		BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));	\
+		kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long)		\
+			(offsetof(typeof(*(ptr)), rhf)));				\
+	}										\
+} while (0)
+
 #define kvfree_rcu_arg_1(ptr)					\
 do {								\
 	typeof(ptr) ___p = (ptr);				\

include/linux/slab.h

@@ -186,6 +186,8 @@ void kfree(const void *);
 void kfree_sensitive(const void *);
 size_t __ksize(const void *);
 size_t ksize(const void *);
+bool kmem_valid_obj(void *object);
+void kmem_dump_obj(void *object);
 
 #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
 void __check_heap_object(const void *ptr, unsigned long n, struct page *page,