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

Pull the latest RCU tree from Paul E. McKenney:

 - Additional cleanups after RCU flavor consolidation
 - Grace-period forward-progress cleanups and improvements
 - Documentation updates
 - Miscellaneous fixes
 - spin_is_locked() conversions to lockdep
 - SPDX changes to RCU source and header files
 - SRCU updates
 - Torture-test updates, including nolibc updates and moving
   nolibc to tools/include

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

Author: Ingo Molnar

Documentation/RCU/Design/Expedited-Grace-Periods/ExpSchedFlow.svg

@@ -72,10 +72,10 @@ <h2><a name="RCU-preempt Expedited Grace Periods">
 in quiescent states.
 Otherwise, the expedited grace period will use
 <tt>smp_call_function_single()</tt> to send the CPU an IPI, which
-is handled by <tt>sync_rcu_exp_handler()</tt>.
+is handled by <tt>rcu_exp_handler()</tt>.
 
 <p>
-However, because this is preemptible RCU, <tt>sync_rcu_exp_handler()</tt>
+However, because this is preemptible RCU, <tt>rcu_exp_handler()</tt>
 can check to see if the CPU is currently running in an RCU read-side
 critical section.
 If not, the handler can immediately report a quiescent state.
@@ -145,19 +145,18 @@ <h2><a name="RCU-sched Expedited Grace Periods">
 <p><img src="ExpSchedFlow.svg" alt="ExpSchedFlow.svg" width="55%">
 
 <p>
-As with RCU-preempt's <tt>synchronize_rcu_expedited()</tt>,
+As with RCU-preempt, RCU-sched's
 <tt>synchronize_sched_expedited()</tt> ignores offline and
 idle CPUs, again because they are in remotely detectable
 quiescent states.
-However, the <tt>synchronize_rcu_expedited()</tt> handler
-is <tt>sync_sched_exp_handler()</tt>, and because the
+However, because the
 <tt>rcu_read_lock_sched()</tt> and <tt>rcu_read_unlock_sched()</tt>
 leave no trace of their invocation, in general it is not possible to tell
 whether or not the current CPU is in an RCU read-side critical section.
-The best that <tt>sync_sched_exp_handler()</tt> can do is to check
+The best that RCU-sched's <tt>rcu_exp_handler()</tt> can do is to check
 for idle, on the off-chance that the CPU went idle while the IPI
 was in flight.
-If the CPU is idle, then <tt>sync_sched_exp_handler()</tt> reports
+If the CPU is idle, then <tt>rcu_exp_handler()</tt> reports
 the quiescent state.
 
 <p> Otherwise, the handler forces a future context switch by setting the
@@ -298,19 +297,18 @@ <h3><a name="Idle-CPU Checks">Idle-CPU Checks</a></h3>
 idle CPUs in the mask passed to <tt>rcu_report_exp_cpu_mult()</tt>.
 
 <p>
-For RCU-sched, there is an additional check for idle in the IPI
-handler, <tt>sync_sched_exp_handler()</tt>.
+For RCU-sched, there is an additional check:
 If the IPI has interrupted the idle loop, then
-<tt>sync_sched_exp_handler()</tt> invokes <tt>rcu_report_exp_rdp()</tt>
+<tt>rcu_exp_handler()</tt> invokes <tt>rcu_report_exp_rdp()</tt>
 to report the corresponding quiescent state.
 
 <p>
 For RCU-preempt, there is no specific check for idle in the
-IPI handler (<tt>sync_rcu_exp_handler()</tt>), but because
+IPI handler (<tt>rcu_exp_handler()</tt>), but because
 RCU read-side critical sections are not permitted within the
-idle loop, if <tt>sync_rcu_exp_handler()</tt> sees that the CPU is within
+idle loop, if <tt>rcu_exp_handler()</tt> sees that the CPU is within
 RCU read-side critical section, the CPU cannot possibly be idle.
-Otherwise, <tt>sync_rcu_exp_handler()</tt> invokes
+Otherwise, <tt>rcu_exp_handler()</tt> invokes
 <tt>rcu_report_exp_rdp()</tt> to report the corresponding quiescent
 state, regardless of whether or not that quiescent state was due to
 the CPU being idle.
@@ -625,6 +623,8 @@ <h3><a name="Mid-Boot Operation">Mid-boot operation</a></h3>
 <p>
 With this refinement, synchronous grace periods can now be used from
 task context pretty much any time during the life of the kernel.
+That is, aside from some points in the suspend, hibernate, or shutdown
+code path.
 
 <h3><a name="Summary">
 Summary</a></h3>

Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html

@@ -485,13 +485,13 @@ <h4><a name="Self-Reported Quiescent States">
 noted by <tt>rcu_node_context_switch()</tt> on the left.
 On the other hand, if the CPU takes a scheduler-clock interrupt
 while executing in usermode, a quiescent state will be noted by
-<tt>rcu_check_callbacks()</tt> on the right.
+<tt>rcu_sched_clock_irq()</tt> on the right.
 Either way, the passage through a quiescent state will be noted
 in a per-CPU variable.
 
 <p>The next time an <tt>RCU_SOFTIRQ</tt> handler executes on
 this CPU (for example, after the next scheduler-clock
-interrupt), <tt>__rcu_process_callbacks()</tt> will invoke
+interrupt), <tt>rcu_core()</tt> will invoke
 <tt>rcu_check_quiescent_state()</tt>, which will notice the
 recorded quiescent state, and invoke
 <tt>rcu_report_qs_rdp()</tt>.
@@ -651,7 +651,7 @@ <h4><a name="Callback Invocation">Callback Invocation</a></h4>
 These callbacks are identified by <tt>rcu_advance_cbs()</tt>,
 which is usually invoked by <tt>__note_gp_changes()</tt>.
 As shown in the diagram below, this invocation can be triggered by
-the scheduling-clock interrupt (<tt>rcu_check_callbacks()</tt> on
+the scheduling-clock interrupt (<tt>rcu_sched_clock_irq()</tt> on
 the left) or by idle entry (<tt>rcu_cleanup_after_idle()</tt> on
 the right, but only for kernels build with
 <tt>CONFIG_RCU_FAST_NO_HZ=y</tt>).

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

@@ -3099,7 +3099,7 @@ <h3><a name="Sleepable RCU">Sleepable RCU</a></h3>
 sections, then that domain's grace periods will also be blocked forever.
 Of course, one good way to block forever is to deadlock, which can
 happen if any operation in a given domain's SRCU read-side critical
-section can block waiting, either directly or indirectly, for that domain's
+section can wait, either directly or indirectly, for that domain's
 grace period to elapse.
 For example, this results in a self-deadlock:
 
@@ -3139,12 +3139,18 @@ <h3><a name="Sleepable RCU">Sleepable RCU</a></h3>
 guarantees a full memory barrier.
 
 <p>
-Also unlike other RCU flavors, SRCU's callbacks-wait function
-<tt>srcu_barrier()</tt> may be invoked from CPU-hotplug notifiers,
-though this is not necessarily a good idea.
-The reason that this is possible is that SRCU is insensitive
-to whether or not a CPU is online, which means that <tt>srcu_barrier()</tt>
-need not exclude CPU-hotplug operations.
+Also unlike other RCU flavors, <tt>synchronize_srcu()</tt> may <b>not</b>
+be invoked from CPU-hotplug notifiers, due to the fact that SRCU grace
+periods make use of timers and the possibility of timers being temporarily
+&ldquo;stranded&rdquo; on the outgoing CPU.
+This stranding of timers means that timers posted to the outgoing CPU
+will not fire until late in the CPU-hotplug process.
+The problem is that if a notifier is waiting on an SRCU grace period,
+that grace period is waiting on a timer, and that timer is stranded on the
+outgoing CPU, then the notifier will never be awakened, in other words,
+deadlock has occurred.
+This same situation of course also prohibits <tt>srcu_barrier()</tt>
+from being invoked from CPU-hotplug notifiers.
 
 <p>
 SRCU also differs from other RCU flavors in that SRCU's expedited and

Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg

@@ -219,17 +219,18 @@ an estimate of the total number of RCU callbacks queued across all CPUs
 In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed
 for each CPU:
 
-	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D
+	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 Nonlazy posted: ..D
 
 The "last_accelerate:" prints the low-order 16 bits (in hex) of the
 jiffies counter when this CPU last invoked rcu_try_advance_all_cbs()
 from rcu_needs_cpu() or last invoked rcu_accelerate_cbs() from
-rcu_prepare_for_idle().  The "nonlazy_posted:" prints the number
-of non-lazy callbacks posted since the last call to rcu_needs_cpu().
-Finally, an "L" indicates that there are currently no non-lazy callbacks
-("." is printed otherwise, as shown above) and "D" indicates that
-dyntick-idle processing is enabled ("." is printed otherwise, for example,
-if disabled via the "nohz=" kernel boot parameter).
+rcu_prepare_for_idle().  The "Nonlazy posted:" indicates lazy-callback
+status, so that an "l" indicates that all callbacks were lazy at the start
+of the last idle period and an "L" indicates that there are currently
+no non-lazy callbacks (in both cases, "." is printed otherwise, as
+shown above) and "D" indicates that dyntick-idle processing is enabled
+("." is printed otherwise, for example, if disabled via the "nohz="
+kernel boot parameter).
 
 If the grace period ends just as the stall warning starts printing,
 there will be a spurious stall-warning message, which will include