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

Pull RCU changes from Paul E. McKenney:

 - Expedited grace-period changes, most notably avoiding having
   user threads drive expedited grace periods, using a workqueue
   instead.

 - Miscellaneous fixes, including a performance fix for lists
   that was sent with the lists modifications (second URL below).

 - CPU hotplug updates, most notably providing exact CPU-online
   tracking for RCU.  This will in turn allow removal of the
   checks supporting RCU's prior heuristic that was based on the
   assumption that CPUs would take no longer than one jiffy to
   come online.

 - Torture-test updates.

 - Documentation updates.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

16 files changed, 193 insertions, 138 deletions

diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index ece410f40436..a4d3838130e4 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -2493,6 +2493,28 @@ or some future “lazy”
 variant of <tt>call_rcu()</tt> that might one day be created for
 energy-efficiency purposes.
 
+<p>
+That said, there are limits.
+RCU requires that the <tt>rcu_head</tt> structure be aligned to a
+two-byte boundary, and passing a misaligned <tt>rcu_head</tt>
+structure to one of the <tt>call_rcu()</tt> family of functions
+will result in a splat.
+It is therefore necessary to exercise caution when packing
+structures containing fields of type <tt>rcu_head</tt>.
+Why not a four-byte or even eight-byte alignment requirement?
+Because the m68k architecture provides only two-byte alignment,
+and thus acts as alignment's least common denominator.
+
+<p>
+The reason for reserving the bottom bit of pointers to
+<tt>rcu_head</tt> structures is to leave the door open to
+&ldquo;lazy&rdquo; callbacks whose invocations can safely be deferred.
+Deferring invocation could potentially have energy-efficiency
+benefits, but only if the rate of non-lazy callbacks decreases
+significantly for some important workload.
+In the meantime, reserving the bottom bit keeps this option open
+in case it one day becomes useful.
+
 <h3><a name="Performance, Scalability, Response Time, and Reliability">
 Performance, Scalability, Response Time, and Reliability</a></h3>
 
diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index 118e7c176ce7..278f6a9383b6 100644
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -10,21 +10,6 @@ status messages via printk(), which can be examined via the dmesg
 command (perhaps grepping for "torture").  The test is started
 when the module is loaded, and stops when the module is unloaded.
 
-CONFIG_RCU_TORTURE_TEST_RUNNABLE
-
-It is also possible to specify CONFIG_RCU_TORTURE_TEST=y, which will
-result in the tests being loaded into the base kernel.  In this case,
-the CONFIG_RCU_TORTURE_TEST_RUNNABLE config option is used to specify
-whether the RCU torture tests are to be started immediately during
-boot or whether the /proc/sys/kernel/rcutorture_runnable file is used
-to enable them.  This /proc file can be used to repeatedly pause and
-restart the tests, regardless of the initial state specified by the
-CONFIG_RCU_TORTURE_TEST_RUNNABLE config option.
-
-You will normally -not- want to start the RCU torture tests during boot
-(and thus the default is CONFIG_RCU_TORTURE_TEST_RUNNABLE=n), but doing
-this can sometimes be useful in finding boot-time bugs.
-
 
 MODULE PARAMETERS
 
diff --git a/include/linux/list.h b/include/linux/list.h
index 5183138aa932..5809e9a2de5b 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -381,8 +381,11 @@ static inline void list_splice_tail_init(struct list_head *list,
  *
  * Note that if the list is empty, it returns NULL.
  */
-#define list_first_entry_or_null(ptr, type, member) \
-        (!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL)
+#define list_first_entry_or_null(ptr, type, member) ({ \
+        struct list_head *head__ = (ptr); \
+        struct list_head *pos__ = READ_ONCE(head__->next); \
+        pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
+})
 
 /**
  * list_next_entry - get the next element in list
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 1aa62e1a761b..321f9ed552a9 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -334,6 +334,7 @@ void rcu_sched_qs(void);
 void rcu_bh_qs(void);
 void rcu_check_callbacks(int user);
 void rcu_report_dead(unsigned int cpu);
+void rcu_cpu_starting(unsigned int cpu);
 
 #ifndef CONFIG_TINY_RCU
 void rcu_end_inkernel_boot(void);
diff --git a/include/linux/torture.h b/include/linux/torture.h
index 6685a73736a2..a45702eb3e7b 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -43,7 +43,7 @@
 
 #define TORTURE_FLAG "-torture:"
 #define TOROUT_STRING(s) \
-        pr_alert("%s" TORTURE_FLAG s "\n", torture_type)
+        pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s)
 #define VERBOSE_TOROUT_STRING(s) \
         do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0)
 #define VERBOSE_TOROUT_ERRSTRING(s) \
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 341bf80f80bd..ff8bc3817dde 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -889,6 +889,7 @@ void notify_cpu_starting(unsigned int cpu)
         struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
         enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
 
+        rcu_cpu_starting(cpu);  /* Enables RCU usage on this CPU. */
         while (st->state < target) {
                 struct cpuhp_step *step;
 
diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
index d38ab08a3fe7..123ccbd22449 100644
--- a/kernel/rcu/rcuperf.c
+++ b/kernel/rcu/rcuperf.c
@@ -52,7 +52,7 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.vnet.ibm.com>");
 
 #define PERF_FLAG "-perf:"
 #define PERFOUT_STRING(s) \
-        pr_alert("%s" PERF_FLAG s "\n", perf_type)
+        pr_alert("%s" PERF_FLAG " %s\n", perf_type, s)
 #define VERBOSE_PERFOUT_STRING(s) \
         do { if (verbose) pr_alert("%s" PERF_FLAG " %s\n", perf_type, s); } while (0)
 #define VERBOSE_PERFOUT_ERRSTRING(s) \
@@ -400,9 +400,8 @@ rcu_perf_writer(void *arg)
                         sp.sched_priority = 0;
                         sched_setscheduler_nocheck(current,
                                                    SCHED_NORMAL, &sp);
-                        pr_alert("%s" PERF_FLAG
-                                 "rcu_perf_writer %ld has %d measurements\n",
-                                 perf_type, me, MIN_MEAS);
+                        pr_alert("%s%s rcu_perf_writer %ld has %d measurements\n",
+                                 perf_type, PERF_FLAG, me, MIN_MEAS);
                         if (atomic_inc_return(&n_rcu_perf_writer_finished) >=
                             nrealwriters) {
                                 schedule_timeout_interruptible(10);
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 971e2b138063..bf08fee53dc7 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1238,6 +1238,7 @@ rcu_torture_stats_print(void)
         long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
         long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
         static unsigned long rtcv_snap = ULONG_MAX;
+        struct task_struct *wtp;
 
         for_each_possible_cpu(cpu) {
                 for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
@@ -1258,8 +1259,9 @@ rcu_torture_stats_print(void)
                 atomic_read(&n_rcu_torture_alloc),
                 atomic_read(&n_rcu_torture_alloc_fail),
                 atomic_read(&n_rcu_torture_free));
-        pr_cont("rtmbe: %d rtbke: %ld rtbre: %ld ",
+        pr_cont("rtmbe: %d rtbe: %ld rtbke: %ld rtbre: %ld ",
                 atomic_read(&n_rcu_torture_mberror),
+                n_rcu_torture_barrier_error,
                 n_rcu_torture_boost_ktrerror,
                 n_rcu_torture_boost_rterror);
         pr_cont("rtbf: %ld rtb: %ld nt: %ld ",
@@ -1312,10 +1314,12 @@ rcu_torture_stats_print(void)
 
                 rcutorture_get_gp_data(cur_ops->ttype,
                                        &flags, &gpnum, &completed);