Merge tag 'rcu.2021.11.01a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU updates from Paul McKenney:

 - Miscellaneous fixes

 - Torture-test updates for smp_call_function(), most notably improved
   checking of module parameters.

 - Tasks-trace RCU updates that fix a number of rare but important
   race-condition bugs.

 - Other torture-test updates, most notably better checking of module
   parameters. In addition, rcutorture may once again be run on
   CONFIG_PREEMPT_RT kernels.

 - Torture-test scripting updates, most notably specifying the new
   CONFIG_KCSAN_STRICT kconfig option rather than maintaining an
   ever-changing list of individual KCSAN kconfig options.

* tag 'rcu.2021.11.01a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (46 commits)
  rcu: Fix rcu_dynticks_curr_cpu_in_eqs() vs noinstr
  rcu: Always inline rcu_dynticks_task*_{enter,exit}()
  torture: Make kvm-remote.sh print size of downloaded tarball
  torture: Allot 1G of memory for scftorture runs
  tools/rcu: Add an extract-stall script
  scftorture: Warn on individual scf_torture_init() error conditions
  scftorture: Count reschedule IPIs
  scftorture: Account for weight_resched when checking for all zeroes
  scftorture: Shut down if nonsensical arguments given
  scftorture: Allow zero weight to exclude an smp_call_function*() category
  rcu: Avoid unneeded function call in rcu_read_unlock()
  rcu-tasks: Update comments to cond_resched_tasks_rcu_qs()
  rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader
  rcu-tasks: Fix read-side primitives comment for call_rcu_tasks_trace
  rcu-tasks: Clarify read side section info for rcu_tasks_rude GP primitives
  rcu-tasks: Correct comparisons for CPU numbers in show_stalled_task_trace
  rcu-tasks: Correct firstreport usage in check_all_holdout_tasks_trace
  rcu-tasks: Fix s/rcu_add_holdout/trc_add_holdout/ typo in comment
  rcu-tasks: Move RTGS_WAIT_CBS to beginning of rcu_tasks_kthread() loop
  rcu-tasks: Fix s/instruction/instructions/ typo in comment
  ...

Author: torvalds

Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst

@@ -202,49 +202,44 @@ newly arrived RCU callbacks against future grace periods:
     1 static void rcu_prepare_for_idle(void)
     2 {
     3   bool needwake;
-    4   struct rcu_data *rdp;
-    5   struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-    6   struct rcu_node *rnp;
-    7   struct rcu_state *rsp;
-    8   int tne;
-    9
-   10   if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) ||
-   11       rcu_is_nocb_cpu(smp_processor_id()))
-   12     return;
+    4   struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+    5   struct rcu_node *rnp;
+    6   int tne;
+    7
+    8   lockdep_assert_irqs_disabled();
+    9   if (rcu_rdp_is_offloaded(rdp))
+   10     return;
+   11
+   12   /* Handle nohz enablement switches conservatively. */
    13   tne = READ_ONCE(tick_nohz_active);
-   14   if (tne != rdtp->tick_nohz_enabled_snap) {
-   15     if (rcu_cpu_has_callbacks(NULL))
-   16       invoke_rcu_core();
-   17     rdtp->tick_nohz_enabled_snap = tne;
+   14   if (tne != rdp->tick_nohz_enabled_snap) {
+   15     if (!rcu_segcblist_empty(&rdp->cblist))
+   16       invoke_rcu_core(); /* force nohz to see update. */
+   17     rdp->tick_nohz_enabled_snap = tne;
    18     return;
-   19   }
+   19	}
    20   if (!tne)
    21     return;
-   22   if (rdtp->all_lazy &&
-   23       rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
-   24     rdtp->all_lazy = false;
-   25     rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
-   26     invoke_rcu_core();
-   27     return;
-   28   }
-   29   if (rdtp->last_accelerate == jiffies)
-   30     return;
-   31   rdtp->last_accelerate = jiffies;
-   32   for_each_rcu_flavor(rsp) {
-   33     rdp = this_cpu_ptr(rsp->rda);
-   34     if (rcu_segcblist_pend_cbs(&rdp->cblist))
-   35       continue;
-   36     rnp = rdp->mynode;
-   37     raw_spin_lock_rcu_node(rnp);
-   38     needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
-   39     raw_spin_unlock_rcu_node(rnp);
-   40     if (needwake)
-   41       rcu_gp_kthread_wake(rsp);
-   42   }
-   43 }
+   22
+   23   /*
+   24    * If we have not yet accelerated this jiffy, accelerate all
+   25    * callbacks on this CPU.
+   26   */
+   27   if (rdp->last_accelerate == jiffies)
+   28     return;
+   29   rdp->last_accelerate = jiffies;
+   30   if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
+   31     rnp = rdp->mynode;
+   32     raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+   33     needwake = rcu_accelerate_cbs(rnp, rdp);
+   34     raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+   35     if (needwake)
+   36       rcu_gp_kthread_wake();
+   37   }
+   38 }
 
 But the only part of ``rcu_prepare_for_idle()`` that really matters for
-this discussion are lines 37–39. We will therefore abbreviate this
+this discussion are lines 32–34. We will therefore abbreviate this
 function as follows:
 
 .. kernel-figure:: rcu_node-lock.svg

Documentation/RCU/stallwarn.rst

@@ -96,6 +96,16 @@ warnings:
 	the ``rcu_.*timer wakeup didn't happen for`` console-log message,
 	which will include additional debugging information.
 
+-	A low-level kernel issue that either fails to invoke one of the
+	variants of rcu_user_enter(), rcu_user_exit(), rcu_idle_enter(),
+	rcu_idle_exit(), rcu_irq_enter(), or rcu_irq_exit() on the one
+	hand, or that invokes one of them too many times on the other.
+	Historically, the most frequent issue has been an omission
+	of either irq_enter() or irq_exit(), which in turn invoke
+	rcu_irq_enter() or rcu_irq_exit(), respectively.  Building your
+	kernel with CONFIG_RCU_EQS_DEBUG=y can help track down these types
+	of issues, which sometimes arise in architecture-specific code.
+
 -	A bug in the RCU implementation.
 
 -	A hardware failure.  This is quite unlikely, but has occurred

arch/sh/configs/sdk7786_defconfig

@@ -5,7 +5,6 @@ CONFIG_BSD_PROCESS_ACCT=y
 CONFIG_BSD_PROCESS_ACCT_V3=y
 CONFIG_AUDIT=y
 CONFIG_AUDITSYSCALL=y
-CONFIG_TREE_PREEMPT_RCU=y
 CONFIG_RCU_TRACE=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y

arch/xtensa/configs/nommu_kc705_defconfig

@@ -119,7 +119,6 @@ CONFIG_DEBUG_SPINLOCK=y
 CONFIG_DEBUG_MUTEXES=y
 CONFIG_DEBUG_ATOMIC_SLEEP=y
 CONFIG_STACKTRACE=y
-# CONFIG_RCU_CPU_STALL_INFO is not set
 CONFIG_RCU_TRACE=y
 # CONFIG_FTRACE is not set
 # CONFIG_LD_NO_RELAX is not set

include/linux/rcupdate.h

@@ -71,7 +71,8 @@ static inline void __rcu_read_lock(void)
 static inline void __rcu_read_unlock(void)
 {
 	preempt_enable();
-	rcu_read_unlock_strict();
+	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+		rcu_read_unlock_strict();
 }
 
 static inline int rcu_preempt_depth(void)

include/linux/rcupdate_trace.h

@@ -31,7 +31,7 @@ static inline int rcu_read_lock_trace_held(void)
 
 #ifdef CONFIG_TASKS_TRACE_RCU
 
-void rcu_read_unlock_trace_special(struct task_struct *t, int nesting);
+void rcu_read_unlock_trace_special(struct task_struct *t);
 
 /**
  * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section
@@ -80,7 +80,8 @@ static inline void rcu_read_unlock_trace(void)
 		WRITE_ONCE(t->trc_reader_nesting, nesting);
 		return;  // We assume shallow reader nesting.
 	}
-	rcu_read_unlock_trace_special(t, nesting);
+	WARN_ON_ONCE(nesting != 0);
+	rcu_read_unlock_trace_special(t);
 }
 
 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);

include/linux/torture.h

@@ -47,6 +47,14 @@ do {										\
 } while (0)
 void verbose_torout_sleep(void);
 
+#define torture_init_error(firsterr)						\
+({										\
+	int ___firsterr = (firsterr);						\
+										\
+	WARN_ONCE(!IS_MODULE(CONFIG_RCU_TORTURE_TEST) && ___firsterr < 0, "Torture-test initialization failed with error code %d\n", ___firsterr); \
+	___firsterr < 0;								\
+})
+
 /* Definitions for online/offline exerciser. */
 #ifdef CONFIG_HOTPLUG_CPU
 int torture_num_online_cpus(void);

kernel/locking/locktorture.c

@@ -1022,23 +1022,23 @@ static int __init lock_torture_init(void)
 	if (onoff_interval > 0) {
 		firsterr = torture_onoff_init(onoff_holdoff * HZ,
 					      onoff_interval * HZ, NULL);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (shuffle_interval > 0) {
 		firsterr = torture_shuffle_init(shuffle_interval);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (shutdown_secs > 0) {
 		firsterr = torture_shutdown_init(shutdown_secs,
 						 lock_torture_cleanup);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (stutter > 0) {
 		firsterr = torture_stutter_init(stutter, stutter);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 
@@ -1082,7 +1082,7 @@ static int __init lock_torture_init(void)
 		/* Create writer. */
 		firsterr = torture_create_kthread(lock_torture_writer, &cxt.lwsa[i],
 						  writer_tasks[i]);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 
 	create_reader:
@@ -1091,13 +1091,13 @@ static int __init lock_torture_init(void)
 		/* Create reader. */
 		firsterr = torture_create_kthread(lock_torture_reader, &cxt.lrsa[j],
 						  reader_tasks[j]);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (stat_interval > 0) {
 		firsterr = torture_create_kthread(lock_torture_stats, NULL,
 						  stats_task);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	torture_init_end();

kernel/rcu/rcuscale.c

@@ -758,7 +758,7 @@ kfree_scale_init(void)
 		init_waitqueue_head(&shutdown_wq);
 		firsterr = torture_create_kthread(kfree_scale_shutdown, NULL,
 						  shutdown_task);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 		schedule_timeout_uninterruptible(1);
 	}
@@ -775,7 +775,7 @@ kfree_scale_init(void)
 	for (i = 0; i < kfree_nrealthreads; i++) {
 		firsterr = torture_create_kthread(kfree_scale_thread, (void *)i,
 						  kfree_reader_tasks[i]);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 
@@ -838,7 +838,7 @@ rcu_scale_init(void)
 		init_waitqueue_head(&shutdown_wq);
 		firsterr = torture_create_kthread(rcu_scale_shutdown, NULL,
 						  shutdown_task);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 		schedule_timeout_uninterruptible(1);
 	}
@@ -852,7 +852,7 @@ rcu_scale_init(void)
 	for (i = 0; i < nrealreaders; i++) {
 		firsterr = torture_create_kthread(rcu_scale_reader, (void *)i,
 						  reader_tasks[i]);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	while (atomic_read(&n_rcu_scale_reader_started) < nrealreaders)
@@ -879,7 +879,7 @@ rcu_scale_init(void)
 		}
 		firsterr = torture_create_kthread(rcu_scale_writer, (void *)i,
 						  writer_tasks[i]);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	torture_init_end();