Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Thomas Gleixner:
 "A large update to RCU:

  Preparatory work for consolidating the RCU flavors:

   - Introduce grace-period sequence numbers to the RCU-bh, RCU-preempt,
     and RCU-sched flavors, replacing the old ->gpnum and ->completed
     pair of fields.

     This change allows lockless code to obtain the complete
     grace-period state with a single READ_ONCE(), which is needed to
     maintain tolerable lock contention during the upcoming
     consolidation of the three RCU flavors.

     Note that grace-period sequence numbers are already used by
     rcu_barrier(), expedited RCU grace periods, and SRCU, and are thus
     already heavily used and well-tested. Joel Fernandes contributed a
     number of excellent fixes and improvements.

   - Clean up some grace-period-reporting loose ends, including
     improving the handling of quiescent states from offline CPUs and
     fixing some false-positive WARN_ON_ONCE() invocations.

     (Strictly speaking, the WARN_ON_ONCE() invocations were quite
     correct, but their invariants were (harmlessly) violated by the
     earlier sloppy handling of quiescent states from offline CPUs.)

     In addition, improve grace-period forward-progress guarantees so as
     to allow removal of fail-safe checks that required otherwise
     needless lock acquisitions. Finally, add more diagnostics to help
     debug the upcoming consolidation of the RCU-bh, RCU-preempt, and
     RCU-sched flavors.

  The rest:

   - SRCU updates

   - Updates to rcutorture and associated scripting.

   - The usual pile of miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (118 commits)
  rcutorture: Fix rcu_barrier successes counter
  rcutorture: Add support to detect if boost kthread prio is too low
  rcutorture: Use monotonic timestamp for stall detection
  rcutorture: Make boost test more robust
  rcutorture: Disable RT throttling for boost tests
  rcutorture: Emphasize testing of single reader protection type
  rcutorture: Handle extended read-side critical sections
  rcutorture: Make rcu_torture_timer() use rcu_torture_one_read()
  rcutorture: Use per-CPU random state for rcu_torture_timer()
  rcutorture: Use atomic increment for n_rcu_torture_timers
  rcutorture: Extract common code from rcu_torture_reader()
  rcuperf: Remove unused torturing_tasks() function
  rcu: Remove rcutorture test version and sequence number
  rcutorture: Change units of onoff_interval to jiffies
  rcu: Assign higher prio to RCU threads if rcutorture is built-in
  rculist: Improve documentation for list_for_each_entry_from_rcu()
  srcu: Add grace-period number to rcutorture statistics printout
  rcu: Print stall-warning NMI dyntick state in hexadecimal
  MAINTAINERS: Update RCU, SRCU, and TORTURE-TEST entries
  rcu: Make rcu_seq_diff() more exact
  ...

Documentation/RCU/Design/Data-Structures/Data-Structures.html

@@ -380,31 +380,26 @@ and therefore need no protection.
 as follows:
 
 <pre>
-  1   unsigned long gpnum;
-  2   unsigned long completed;
+  1   unsigned long gp_seq;
 </pre>
 
 <p>RCU grace periods are numbered, and
-the <tt>-&gt;gpnum</tt> field contains the number of the grace
-period that started most recently.
-The <tt>-&gt;completed</tt> field contains the number of the
-grace period that completed most recently.
-If the two fields are equal, the RCU grace period that most recently
-started has already completed, and therefore the corresponding
-flavor of RCU is idle.
-If <tt>-&gt;gpnum</tt> is one greater than <tt>-&gt;completed</tt>,
-then <tt>-&gt;gpnum</tt> gives the number of the current RCU
-grace period, which has not yet completed.
-Any other combination of values indicates that something is broken.
-These two fields are protected by the root <tt>rcu_node</tt>'s
+the <tt>-&gt;gp_seq</tt> field contains the current grace-period
+sequence number.
+The bottom two bits are the state of the current grace period,
+which can be zero for not yet started or one for in progress.
+In other words, if the bottom two bits of <tt>-&gt;gp_seq</tt> are
+zero, the corresponding flavor of RCU is idle.
+Any other value in the bottom two bits indicates that something is broken.
+This field is protected by the root <tt>rcu_node</tt> structure's
 <tt>-&gt;lock</tt> field.
 
-</p><p>There are <tt>-&gt;gpnum</tt> and <tt>-&gt;completed</tt> fields
+</p><p>There are <tt>-&gt;gp_seq</tt> fields
 in the <tt>rcu_node</tt> and <tt>rcu_data</tt> structures
 as well.
 The fields in the <tt>rcu_state</tt> structure represent the
-most current values, and those of the other structures are compared
-in order to detect the start of a new grace period in a distributed
+most current value, and those of the other structures are compared
+in order to detect the beginnings and ends of grace periods in a distributed
 fashion.
 The values flow from <tt>rcu_state</tt> to <tt>rcu_node</tt>
 (down the tree from the root to the leaves) to <tt>rcu_data</tt>.
@@ -512,27 +507,47 @@ than to be heisenbugged out of existence.
 as follows:
 
 <pre>
-  1   unsigned long gpnum;
-  2   unsigned long completed;
+  1   unsigned long gp_seq;
+  2   unsigned long gp_seq_needed;
 </pre>
 
-<p>These fields are the counterparts of the fields of the same name in
-the <tt>rcu_state</tt> structure.
-They each may lag up to one behind their <tt>rcu_state</tt>
-counterparts.
-If a given <tt>rcu_node</tt> structure's <tt>-&gt;gpnum</tt> and
-<tt>-&gt;complete</tt> fields are equal, then this <tt>rcu_node</tt>
+<p>The <tt>rcu_node</tt> structures' <tt>-&gt;gp_seq</tt> fields are
+the counterparts of the field of the same name in the <tt>rcu_state</tt>
+structure.
+They each may lag up to one step behind their <tt>rcu_state</tt>
+counterpart.
+If the bottom two bits of a given <tt>rcu_node</tt> structure's
+<tt>-&gt;gp_seq</tt> field is zero, then this <tt>rcu_node</tt>
 structure believes that RCU is idle.
-Otherwise, as with the <tt>rcu_state</tt> structure,
-the <tt>-&gt;gpnum</tt> field will be one greater than the
-<tt>-&gt;complete</tt> fields, with <tt>-&gt;gpnum</tt>
-indicating which grace period this <tt>rcu_node</tt> believes
-is still being waited for.
+</p><p>The <tt>&gt;gp_seq</tt> field of each <tt>rcu_node</tt>
+structure is updated at the beginning and the end
+of each grace period.
+
+<p>The <tt>-&gt;gp_seq_needed</tt> fields record the
+furthest-in-the-future grace period request seen by the corresponding
+<tt>rcu_node</tt> structure.  The request is considered fulfilled when
+the value of the <tt>-&gt;gp_seq</tt> field equals or exceeds that of
+the <tt>-&gt;gp_seq_needed</tt> field.
 
-</p><p>The <tt>&gt;gpnum</tt> field of each <tt>rcu_node</tt>
-structure is updated at the beginning
-of each grace period, and the <tt>-&gt;completed</tt> fields are
-updated at the end of each grace period.
+<table>
+<tr><th>&nbsp;</th></tr>
+<tr><th align="left">Quick Quiz:</th></tr>
+<tr><td>
+	Suppose that this <tt>rcu_node</tt> structure doesn't see
+	a request for a very long time.
+	Won't wrapping of the <tt>-&gt;gp_seq</tt> field cause
+	problems?
+</td></tr>
+<tr><th align="left">Answer:</th></tr>
+<tr><td bgcolor="#ffffff"><font color="ffffff">
+	No, because if the <tt>-&gt;gp_seq_needed</tt> field lags behind the
+	<tt>-&gt;gp_seq</tt> field, the <tt>-&gt;gp_seq_needed</tt> field
+	will be updated at the end of the grace period.
+	Modulo-arithmetic comparisons therefore will always get the
+	correct answer, even with wrapping.
+</font></td></tr>
+<tr><td>&nbsp;</td></tr>
+</table>
 
 <h5>Quiescent-State Tracking</h5>
 
@@ -626,9 +641,8 @@ normal and expedited grace periods, respectively.
 	</ol>
 
 	<p><font color="ffffff">So the locking is absolutely required in
-	order to coordinate
-	clearing of the bits with the grace-period numbers in
-	<tt>-&gt;gpnum</tt> and <tt>-&gt;completed</tt>.
+	order to coordinate clearing of the bits with updating of the
+	grace-period sequence number in <tt>-&gt;gp_seq</tt>.
 </font></td></tr>
 <tr><td>&nbsp;</td></tr>
 </table>
@@ -1038,15 +1052,15 @@ out any <tt>rcu_data</tt> structure for which this flag is not set.
 as follows:
 
 <pre>
-  1   unsigned long completed;
-  2   unsigned long gpnum;
+  1   unsigned long gp_seq;
+  2   unsigned long gp_seq_needed;
   3   bool cpu_no_qs;
   4   bool core_needs_qs;
   5   bool gpwrap;
   6   unsigned long rcu_qs_ctr_snap;
 </pre>
 
-<p>The <tt>completed</tt> and <tt>gpnum</tt>
+<p>The <tt>-&gt;gp_seq</tt> and <tt>-&gt;gp_seq_needed</tt>
 fields are the counterparts of the fields of the same name
 in the <tt>rcu_state</tt> and <tt>rcu_node</tt> structures.
 They may each lag up to one behind their <tt>rcu_node</tt>
@@ -1054,15 +1068,9 @@ counterparts, but in <tt>CONFIG_NO_HZ_IDLE</tt> and
 <tt>CONFIG_NO_HZ_FULL</tt> kernels can lag
 arbitrarily far behind for CPUs in dyntick-idle mode (but these counters
 will catch up upon exit from dyntick-idle mode).
-If a given <tt>rcu_data</tt> structure's <tt>-&gt;gpnum</tt> and
-<tt>-&gt;complete</tt> fields are equal, then this <tt>rcu_data</tt>
+If the lower two bits of a given <tt>rcu_data</tt> structure's
+<tt>-&gt;gp_seq</tt> are zero, then this <tt>rcu_data</tt>
 structure believes that RCU is idle.
-Otherwise, as with the <tt>rcu_state</tt> and <tt>rcu_node</tt>
-structure,
-the <tt>-&gt;gpnum</tt> field will be one greater than the
-<tt>-&gt;complete</tt> fields, with <tt>-&gt;gpnum</tt>
-indicating which grace period this <tt>rcu_data</tt> believes
-is still being waited for.
 
 <table>
 <tr><th>&nbsp;</th></tr>
@@ -1070,13 +1078,13 @@ is still being waited for.
 <tr><td>
 	All this replication of the grace period numbers can only cause
 	massive confusion.
-	Why not just keep a global pair of counters and be done with it???
+	Why not just keep a global sequence number and be done with it???
 </td></tr>
 <tr><th align="left">Answer:</th></tr>
 <tr><td bgcolor="#ffffff"><font color="ffffff">
-	Because if there was only a single global pair of grace-period
+	Because if there was only a single global sequence
 	numbers, there would need to be a single global lock to allow
-	safely accessing and updating them.
+	safely accessing and updating it.
 	And if we are not going to have a single global lock, we need
 	to carefully manage the numbers on a per-node basis.
 	Recall from the answer to a previous Quick Quiz that the consequences
@@ -1091,8 +1099,8 @@ CPU has not yet passed through a quiescent state,
 while the <tt>-&gt;core_needs_qs</tt> flag indicates that the
 RCU core needs a quiescent state from the corresponding CPU.
 The <tt>-&gt;gpwrap</tt> field indicates that the corresponding
-CPU has remained idle for so long that the <tt>completed</tt>
-and <tt>gpnum</tt> counters are in danger of overflow, which
+CPU has remained idle for so long that the
+<tt>gp_seq</tt> counter is in danger of overflow, which
 will cause the CPU to disregard the values of its counters on
 its next exit from idle.
 Finally, the <tt>rcu_qs_ctr_snap</tt> field is used to detect
@@ -1130,10 +1138,10 @@ The CPU advances the callbacks in its <tt>rcu_data</tt> structure
 whenever it notices that another RCU grace period has completed.
 The CPU detects the completion of an RCU grace period by noticing
 that the value of its <tt>rcu_data</tt> structure's
-<tt>-&gt;completed</tt> field differs from that of its leaf
+<tt>-&gt;gp_seq</tt> field differs from that of its leaf
 <tt>rcu_node</tt> structure.
 Recall that each <tt>rcu_node</tt> structure's
-<tt>-&gt;completed</tt> field is updated at the end of each
+<tt>-&gt;gp_seq</tt> field is updated at the beginnings and ends of each
 grace period.
 
 <p>

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

@@ -357,7 +357,7 @@ parts, starting in this section with the various phases of
 grace-period initialization.
 
 <p>The first ordering-related grace-period initialization action is to
-increment the <tt>rcu_state</tt> structure's <tt>-&gt;gpnum</tt>
+advance the <tt>rcu_state</tt> structure's <tt>-&gt;gp_seq</tt>
 grace-period-number counter, as shown below:
 
 </p><p><img src="TreeRCU-gp-init-1.svg" alt="TreeRCU-gp-init-1.svg" width="75%">
@@ -388,7 +388,7 @@ its last CPU and if the next <tt>rcu_node</tt> structure has no online CPUs).
 
 <p>The final <tt>rcu_gp_init()</tt> pass through the <tt>rcu_node</tt>
 tree traverses breadth-first, setting each <tt>rcu_node</tt> structure's
-<tt>-&gt;gpnum</tt> field to the newly incremented value from the
+<tt>-&gt;gp_seq</tt> field to the newly advanced value from the
 <tt>rcu_state</tt> structure, as shown in the following diagram.
 
 </p><p><img src="TreeRCU-gp-init-3.svg" alt="TreeRCU-gp-init-1.svg" width="75%">
@@ -398,9 +398,9 @@ tree traverses breadth-first, setting each <tt>rcu_node</tt> structure's
 to notice that a new grace period has started, as described in the next
 section.
 But because the grace-period kthread started the grace period at the
-root (with the increment of the <tt>rcu_state</tt> structure's
-<tt>-&gt;gpnum</tt> field) before setting each leaf <tt>rcu_node</tt>
-structure's <tt>-&gt;gpnum</tt> field, each CPU's observation of
+root (with the advancing of the <tt>rcu_state</tt> structure's
+<tt>-&gt;gp_seq</tt> field) before setting each leaf <tt>rcu_node</tt>
+structure's <tt>-&gt;gp_seq</tt> field, each CPU's observation of
 the start of the grace period will happen after the actual start
 of the grace period.
 
@@ -466,7 +466,7 @@ section that the grace period must wait on.
 <tr><td>
 	But a RCU read-side critical section might have started
 	after the beginning of the grace period
-	(the <tt>-&gt;gpnum++</tt> from earlier), so why should
+	(the advancing of <tt>-&gt;gp_seq</tt> from earlier), so why should
 	the grace period wait on such a critical section?
 </td></tr>
 <tr><th align="left">Answer:</th></tr>
@@ -609,10 +609,8 @@ states outstanding from other CPUs.
 <h4><a name="Grace-Period Cleanup">Grace-Period Cleanup</a></h4>
 
 <p>Grace-period cleanup first scans the <tt>rcu_node</tt> tree
-breadth-first setting all the <tt>-&gt;completed</tt> fields equal
-to the number of the newly completed grace period, then it sets
-the <tt>rcu_state</tt> structure's <tt>-&gt;completed</tt> field,
-again to the number of the newly completed grace period.
+breadth-first advancing all the <tt>-&gt;gp_seq</tt> fields, then it
+advances the <tt>rcu_state</tt> structure's <tt>-&gt;gp_seq</tt> field.
 The ordering effects are shown below:
 
 </p><p><img src="TreeRCU-gp-cleanup.svg" alt="TreeRCU-gp-cleanup.svg" width="75%">
@@ -634,7 +632,7 @@ grace-period cleanup is complete, the next grace period can begin.
 	CPU has reported its quiescent state, but it may be some
 	milliseconds before RCU becomes aware of this.
 	The latest reasonable candidate is once the <tt>rcu_state</tt>
-	structure's <tt>-&gt;completed</tt> field has been updated,
+	structure's <tt>-&gt;gp_seq</tt> field has been updated,
 	but it is quite possible that some CPUs have already completed
 	phase two of their updates by that time.
 	In short, if you are going to work with RCU, you need to
@@ -647,7 +645,7 @@ grace-period cleanup is complete, the next grace period can begin.
 <h4><a name="Callback Invocation">Callback Invocation</a></h4>
 
 <p>Once a given CPU's leaf <tt>rcu_node</tt> structure's
-<tt>-&gt;completed</tt> field has been updated, that CPU can begin
+<tt>-&gt;gp_seq</tt> field has been updated, that CPU can begin
 invoking its RCU callbacks that were waiting for this grace period
 to end.
 These callbacks are identified by <tt>rcu_advance_cbs()</tt>,

Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-cleanup.svg

@@ -384,11 +384,11 @@
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+       id="text202-36-2"
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@@ -1019,13 +1022,15 @@
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+         style="font-size:172.87567139px"
+         id="tspan3166-56">rcu_seq_end(&amp;rnp-&gt;gp_seq)</tspan></text>
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+       style="font-size:172.87567139px"
+       id="tspan3166-2">rcu_seq_end(&amp;rnp-&gt;gp_seq)</tspan></text>
 </svg>

Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-init-1.svg

@@ -272,13 +272,13 @@
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+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;font-family:Courier"><tspan
+         style="font-size:172.87567139px"
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Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-init-3.svg

@@ -19,7 +19,7 @@
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@@ -281,13 +285,13 @@
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-       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;font-family:Courier">-&gt;gpnum = rsp-&gt;gpnum</text>
+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
     <g
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@@ -366,13 +370,13 @@
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+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
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@@ -413,13 +417,13 @@
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        font-size="192"
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+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
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@@ -448,13 +452,13 @@
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+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
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+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
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+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
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+     style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">-&gt;gp_seq = rsp-&gt;gp_seq</text>
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Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg

@@ -300,13 +300,13 @@
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-     inkscape:zoom="0.70710678"
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+         style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rdp-&gt;gp_seq</text>
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Documentation/RCU/stallwarn.txt

@@ -172,7 +172,7 @@ it will print a message similar to the following:
 	INFO: rcu_sched detected stalls on CPUs/tasks:
 	2-...: (3 GPs behind) idle=06c/0/0 softirq=1453/1455 fqs=0
 	16-...: (0 ticks this GP) idle=81c/0/0 softirq=764/764 fqs=0
-	(detected by 32, t=2603 jiffies, g=7073, c=7072, q=625)
+	(detected by 32, t=2603 jiffies, g=7075, q=625)
 
 This message indicates that CPU 32 detected that CPUs 2 and 16 were both
 causing stalls, and that the stall was affecting RCU-sched.  This message
@@ -215,11 +215,10 @@ CPU since the last time that this CPU noted the beginning of a grace
 period.
 
 The "detected by" line indicates which CPU detected the stall (in this
-case, CPU 32), how many jiffies have elapsed since the start of the
-grace period (in this case 2603), the number of the last grace period
-to start and to complete (7073 and 7072, respectively), and an estimate
-of the total number of RCU callbacks queued across all CPUs (625 in
-this case).
+case, CPU 32), how many jiffies have elapsed since the start of the grace
+period (in this case 2603), the grace-period sequence number (7075), and
+an estimate of the total number of RCU callbacks queued across all CPUs
+(625 in this case).
 
 In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed
 for each CPU:
@@ -266,15 +265,16 @@ If the relevant grace-period kthread has been unable to run prior to
 the stall warning, as was the case in the "All QSes seen" line above,
 the following additional line is printed:
 
-	kthread starved for 23807 jiffies! g7073 c7072 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1
+	kthread starved for 23807 jiffies! g7075 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 ->cpu=5
 
 Starving the grace-period kthreads of CPU time can of course result
 in RCU CPU stall warnings even when all CPUs and tasks have passed
-through the required quiescent states.  The "g" and "c" numbers flag the
-number of the last grace period started and completed, respectively,
-the "f" precedes the ->gp_flags command to the grace-period kthread,
-the "RCU_GP_WAIT_FQS" indicates that the kthread is waiting for a short
-timeout, and the "state" precedes value of the task_struct ->state field.
+through the required quiescent states.  The "g" number shows the current
+grace-period sequence number, the "f" precedes the ->gp_flags command
+to the grace-period kthread, the "RCU_GP_WAIT_FQS" indicates that the
+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.
 
 
 Multiple Warnings From One Stall

Documentation/RCU/whatisRCU.txt

@@ -588,6 +588,7 @@ It is extremely simple:
 	void synchronize_rcu(void)
 	{
 		write_lock(&rcu_gp_mutex);
+		smp_mb__after_spinlock();
 		write_unlock(&rcu_gp_mutex);
 	}
 
@@ -609,12 +610,15 @@ don't forget about them when submitting patches making use of RCU!]
 
 The rcu_read_lock() and rcu_read_unlock() primitive read-acquire
 and release a global reader-writer lock.  The synchronize_rcu()
-primitive write-acquires this same lock, then immediately releases
-it.  This means that once synchronize_rcu() exits, all RCU read-side
-critical sections that were in progress before synchronize_rcu() was
-called are guaranteed to have completed -- there is no way that
-synchronize_rcu() would have been able to write-acquire the lock
-otherwise.
+primitive write-acquires this same lock, then releases it.  This means
+that once synchronize_rcu() exits, all RCU read-side critical sections
+that were in progress before synchronize_rcu() was called are guaranteed
+to have completed -- there is no way that synchronize_rcu() would have
+been able to write-acquire the lock otherwise.  The smp_mb__after_spinlock()
+promotes synchronize_rcu() to a full memory barrier in compliance with
+the "Memory-Barrier Guarantees" listed in:
+
+	Documentation/RCU/Design/Requirements/Requirements.html.
 
 It is possible to nest rcu_read_lock(), since reader-writer locks may
 be recursively acquired.  Note also that rcu_read_lock() is immune
@@ -816,11 +820,13 @@ RCU list traversal:
 	list_next_rcu
 	list_for_each_entry_rcu
 	list_for_each_entry_continue_rcu
+	list_for_each_entry_from_rcu
 	hlist_first_rcu
 	hlist_next_rcu
 	hlist_pprev_rcu
 	hlist_for_each_entry_rcu
 	hlist_for_each_entry_rcu_bh
+	hlist_for_each_entry_from_rcu
 	hlist_for_each_entry_continue_rcu
 	hlist_for_each_entry_continue_rcu_bh
 	hlist_nulls_first_rcu

Documentation/admin-guide/kernel-parameters.txt

@@ -3632,8 +3632,8 @@
 			Set time (s) after boot for CPU-hotplug testing.
 
 	rcutorture.onoff_interval= [KNL]
-			Set time (s) between CPU-hotplug operations, or
-			zero to disable CPU-hotplug testing.
+			Set time (jiffies) between CPU-hotplug operations,
+			or zero to disable CPU-hotplug testing.
 
 	rcutorture.shuffle_interval= [KNL]
 			Set task-shuffle interval (s).  Shuffling tasks

MAINTAINERS

@@ -12039,9 +12039,9 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
 F:	Documentation/RCU/
 X:	Documentation/RCU/torture.txt
 F:	include/linux/rcu*
-X:	include/linux/srcu.h
+X:	include/linux/srcu*.h
 F:	kernel/rcu/
-X:	kernel/torture.c
+X:	kernel/rcu/srcu*.c
 
 REAL TIME CLOCK (RTC) SUBSYSTEM
 M:	Alessandro Zummo <a.zummo@towertech.it>
@@ -13078,8 +13078,8 @@ L:	linux-kernel@vger.kernel.org
 W:	http://www.rdrop.com/users/paulmck/RCU/
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
-F:	include/linux/srcu.h
-F:	kernel/rcu/srcu.c
+F:	include/linux/srcu*.h
+F:	kernel/rcu/srcu*.c
 
 SERIAL LOW-POWER INTER-CHIP MEDIA BUS (SLIMbus)
 M:	Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
@@ -14438,6 +14438,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
 F:	Documentation/RCU/torture.txt
 F:	kernel/torture.c
 F:	kernel/rcu/rcutorture.c
+F:	kernel/rcu/rcuperf.c
 F:	kernel/locking/locktorture.c
 
 TOSHIBA ACPI EXTRAS DRIVER

include/linux/rculist.h

@@ -396,7 +396,16 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * @member:	the name of the list_head within the struct.
  *
  * Continue to iterate over list of given type, continuing after
- * the current position.
+ * the current position which must have been in the list when the RCU read
+ * lock was taken.
+ * This would typically require either that you obtained the node from a
+ * previous walk of the list in the same RCU read-side critical section, or
+ * that you held some sort of non-RCU reference (such as a reference count)
+ * to keep the node alive *and* in the list.
+ *
+ * This iterator is similar to list_for_each_entry_from_rcu() except
+ * this starts after the given position and that one starts at the given
+ * position.
  */
 #define list_for_each_entry_continue_rcu(pos, head, member) 		\
 	for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
@@ -411,6 +420,14 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  *
  * Iterate over the tail of a list starting from a given position,
  * which must have been in the list when the RCU read lock was taken.
+ * This would typically require either that you obtained the node from a
+ * previous walk of the list in the same RCU read-side critical section, or
+ * that you held some sort of non-RCU reference (such as a reference count)
+ * to keep the node alive *and* in the list.
+ *
+ * This iterator is similar to list_for_each_entry_continue_rcu() except
+ * this starts from the given position and that one starts from the position
+ * after the given position.
  */
 #define list_for_each_entry_from_rcu(pos, head, member)			\
 	for (; &(pos)->member != (head);					\

include/linux/rcupdate.h

@@ -64,7 +64,6 @@ void rcu_barrier_tasks(void);
 
 void __rcu_read_lock(void);
 void __rcu_read_unlock(void);
-void rcu_read_unlock_special(struct task_struct *t);
 void synchronize_rcu(void);
 
 /*
@@ -159,11 +158,11 @@ static inline void rcu_init_nohz(void) { }
 	} while (0)
 
 /*
- * Note a voluntary context switch for RCU-tasks benefit.  This is a
- * macro rather than an inline function to avoid #include hell.
+ * Note a quasi-voluntary context switch for RCU-tasks's benefit.
+ * This is a macro rather than an inline function to avoid #include hell.
  */
 #ifdef CONFIG_TASKS_RCU
-#define rcu_note_voluntary_context_switch_lite(t) \
+#define rcu_tasks_qs(t) \
 	do { \
 		if (READ_ONCE((t)->rcu_tasks_holdout)) \
 			WRITE_ONCE((t)->rcu_tasks_holdout, false); \
@@ -171,14 +170,14 @@ static inline void rcu_init_nohz(void) { }
 #define rcu_note_voluntary_context_switch(t) \
 	do { \
 		rcu_all_qs(); \
-		rcu_note_voluntary_context_switch_lite(t); \
+		rcu_tasks_qs(t); \
 	} while (0)
 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
 void synchronize_rcu_tasks(void);
 void exit_tasks_rcu_start(void);
 void exit_tasks_rcu_finish(void);
 #else /* #ifdef CONFIG_TASKS_RCU */
-#define rcu_note_voluntary_context_switch_lite(t)	do { } while (0)
+#define rcu_tasks_qs(t)	do { } while (0)
 #define rcu_note_voluntary_context_switch(t)		rcu_all_qs()
 #define call_rcu_tasks call_rcu_sched
 #define synchronize_rcu_tasks synchronize_sched
@@ -195,8 +194,8 @@ static inline void exit_tasks_rcu_finish(void) { }
  */
 #define cond_resched_tasks_rcu_qs() \
 do { \
-	if (!cond_resched()) \
-		rcu_note_voluntary_context_switch_lite(current); \
+	rcu_tasks_qs(current); \
+	cond_resched(); \
 } while (0)
 
 /*
@@ -567,8 +566,8 @@ static inline void rcu_preempt_sleep_check(void) { }
  * 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:
- * ``
+ * kill_dependency().  It could be used as follows::
+ *
  *	rcu_read_lock();
  *	p = rcu_dereference(gp);
  *	long_lived = is_long_lived(p);
@@ -579,7 +578,6 @@ static inline void rcu_preempt_sleep_check(void) { }
  *			p = rcu_pointer_handoff(p);
  *	}
  *	rcu_read_unlock();
- *``
  */
 #define rcu_pointer_handoff(p) (p)
 

include/linux/rcutiny.h

@@ -93,7 +93,7 @@ static inline void kfree_call_rcu(struct rcu_head *head,
 #define rcu_note_context_switch(preempt) \
 	do { \
 		rcu_sched_qs(); \
-		rcu_note_voluntary_context_switch_lite(current); \
+		rcu_tasks_qs(current); \
 	} while (0)
 
 static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)

include/linux/srcu.h

@@ -195,6 +195,16 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 	return retval;
 }
 
+/* Used by tracing, cannot be traced and cannot invoke lockdep. */
+static inline notrace int
+srcu_read_lock_notrace(struct srcu_struct *sp) __acquires(sp)
+{
+	int retval;
+
+	retval = __srcu_read_lock(sp);
+	return retval;
+}
+
 /**
  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
  * @sp: srcu_struct in which to unregister the old reader.
@@ -209,6 +219,13 @@ static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 	__srcu_read_unlock(sp, idx);
 }
 
+/* Used by tracing, cannot be traced and cannot call lockdep. */
+static inline notrace void
+srcu_read_unlock_notrace(struct srcu_struct *sp, int idx) __releases(sp)
+{
+	__srcu_read_unlock(sp, idx);
+}
+
 /**
  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
  *

include/linux/torture.h

@@ -64,6 +64,8 @@ struct torture_random_state {
 	long trs_count;
 };
 #define DEFINE_TORTURE_RANDOM(name) struct torture_random_state name = { 0, 0 }
+#define DEFINE_TORTURE_RANDOM_PERCPU(name) \
+	DEFINE_PER_CPU(struct torture_random_state, name)
 unsigned long torture_random(struct torture_random_state *trsp);
 
 /* Task shuffler, which causes CPUs to occasionally go idle. */
@@ -79,7 +81,7 @@ void stutter_wait(const char *title);
 int torture_stutter_init(int s);
 
 /* Initialization and cleanup. */
-bool torture_init_begin(char *ttype, bool v);
+bool torture_init_begin(char *ttype, int v);
 void torture_init_end(void);
 bool torture_cleanup_begin(void);
 void torture_cleanup_end(void);

kernel/locking/locktorture.c

@@ -21,6 +21,9 @@
  *          Davidlohr Bueso <dave@stgolabs.net>
  *	Based on kernel/rcu/torture.c.
  */
+
+#define pr_fmt(fmt) fmt
+
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/kthread.h>
@@ -57,7 +60,7 @@ torture_param(int, shutdown_secs, 0, "Shutdown time (j), <= zero to disable.");
 torture_param(int, stat_interval, 60,
 	     "Number of seconds between stats printk()s");
 torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
-torture_param(bool, verbose, true,
+torture_param(int, verbose, 1,
 	     "Enable verbose debugging printk()s");
 
 static char *torture_type = "spin_lock";

kernel/rcu/rcu.h

@@ -91,7 +91,17 @@ static inline void rcu_seq_end(unsigned long *sp)
 	WRITE_ONCE(*sp, rcu_seq_endval(sp));
 }
 
-/* Take a snapshot of the update side's sequence number. */
+/*
+ * rcu_seq_snap - Take a snapshot of the update side's sequence number.
+ *
+ * This function returns the earliest value of the grace-period sequence number
+ * that will indicate that a full grace period has elapsed since the current
+ * time.  Once the grace-period sequence number has reached this value, it will
+ * be safe to invoke all callbacks that have been registered prior to the
+ * current time. This value is the current grace-period number plus two to the
+ * power of the number of low-order bits reserved for state, then rounded up to
+ * the next value in which the state bits are all zero.
+ */
 static inline unsigned long rcu_seq_snap(unsigned long *sp)
 {
 	unsigned long s;
@@ -107,6 +117,15 @@ static inline unsigned long rcu_seq_current(unsigned long *sp)
 	return READ_ONCE(*sp);
 }
 
+/*
+ * Given a snapshot from rcu_seq_snap(), determine whether or not the
+ * corresponding update-side operation has started.
+ */
+static inline bool rcu_seq_started(unsigned long *sp, unsigned long s)
+{
+	return ULONG_CMP_LT((s - 1) & ~RCU_SEQ_STATE_MASK, READ_ONCE(*sp));
+}
+
 /*
  * Given a snapshot from rcu_seq_snap(), determine whether or not a
  * full update-side operation has occurred.
@@ -116,6 +135,45 @@ static inline bool rcu_seq_done(unsigned long *sp, unsigned long s)
 	return ULONG_CMP_GE(READ_ONCE(*sp), s);
 }
 
+/*
+ * Has a grace period completed since the time the old gp_seq was collected?
+ */
+static inline bool rcu_seq_completed_gp(unsigned long old, unsigned long new)
+{
+	return ULONG_CMP_LT(old, new & ~RCU_SEQ_STATE_MASK);
+}
+
+/*
+ * Has a grace period started since the time the old gp_seq was collected?
+ */
+static inline bool rcu_seq_new_gp(unsigned long old, unsigned long new)
+{
+	return ULONG_CMP_LT((old + RCU_SEQ_STATE_MASK) & ~RCU_SEQ_STATE_MASK,
+			    new);
+}
+
+/*
+ * Roughly how many full grace periods have elapsed between the collection
+ * of the two specified grace periods?
+ */
+static inline unsigned long rcu_seq_diff(unsigned long new, unsigned long old)
+{
+	unsigned long rnd_diff;
+
+	if (old == new)
+		return 0;
+	/*
+	 * Compute the number of grace periods (still shifted up), plus
+	 * one if either of new and old is not an exact grace period.
+	 */
+	rnd_diff = (new & ~RCU_SEQ_STATE_MASK) -
+		   ((old + RCU_SEQ_STATE_MASK) & ~RCU_SEQ_STATE_MASK) +
+		   ((new & RCU_SEQ_STATE_MASK) || (old & RCU_SEQ_STATE_MASK));
+	if (ULONG_CMP_GE(RCU_SEQ_STATE_MASK, rnd_diff))
+		return 1; /* Definitely no grace period has elapsed. */
+	return ((rnd_diff - RCU_SEQ_STATE_MASK - 1) >> RCU_SEQ_CTR_SHIFT) + 2;
+}
+
 /*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
  * by call_rcu() and rcu callback execution, and are therefore not part of the
@@ -276,6 +334,9 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt)
 /* Is this rcu_node a leaf? */
 #define rcu_is_leaf_node(rnp) ((rnp)->level == rcu_num_lvls - 1)
 
+/* Is this rcu_node the last leaf? */
+#define rcu_is_last_leaf_node(rsp, rnp) ((rnp) == &(rsp)->node[rcu_num_nodes - 1])
+
 /*
  * Do a full breadth-first scan of the rcu_node structures for the
  * specified rcu_state structure.
@@ -405,8 +466,7 @@ enum rcutorture_type {
 
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
-			    unsigned long *gpnum, unsigned long *completed);
-void rcutorture_record_test_transition(void);
+			    unsigned long *gp_seq);
 void rcutorture_record_progress(unsigned long vernum);
 void do_trace_rcu_torture_read(const char *rcutorturename,
 			       struct rcu_head *rhp,
@@ -415,15 +475,11 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 			       unsigned long c);
 #else
 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
-					  int *flags,
-					  unsigned long *gpnum,
-					  unsigned long *completed)
+					  int *flags, unsigned long *gp_seq)
 {
 	*flags = 0;
-	*gpnum = 0;
-	*completed = 0;
+	*gp_seq = 0;
 }
-static inline void rcutorture_record_test_transition(void) { }
 static inline void rcutorture_record_progress(unsigned long vernum) { }
 #ifdef CONFIG_RCU_TRACE
 void do_trace_rcu_torture_read(const char *rcutorturename,
@@ -441,31 +497,26 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
 
 static inline void srcutorture_get_gp_data(enum rcutorture_type test_type,
 					   struct srcu_struct *sp, int *flags,
-					   unsigned long *gpnum,
-					   unsigned long *completed)
+					   unsigned long *gp_seq)
 {
 	if (test_type != SRCU_FLAVOR)
 		return;
 	*flags = 0;
-	*completed = sp->srcu_idx;
-	*gpnum = *completed;
+	*gp_seq = sp->srcu_idx;
 }
 
 #elif defined(CONFIG_TREE_SRCU)
 
 void srcutorture_get_gp_data(enum rcutorture_type test_type,
 			     struct srcu_struct *sp, int *flags,
-			     unsigned long *gpnum, unsigned long *completed);
+			     unsigned long *gp_seq);
 
 #endif
 
 #ifdef CONFIG_TINY_RCU
-static inline unsigned long rcu_batches_started(void) { return 0; }
-static inline unsigned long rcu_batches_started_bh(void) { return 0; }
-static inline unsigned long rcu_batches_started_sched(void) { return 0; }
-static inline unsigned long rcu_batches_completed(void) { return 0; }
-static inline unsigned long rcu_batches_completed_bh(void) { return 0; }
-static inline unsigned long rcu_batches_completed_sched(void) { return 0; }
+static inline unsigned long rcu_get_gp_seq(void) { return 0; }
+static inline unsigned long rcu_bh_get_gp_seq(void) { return 0; }
+static inline unsigned long rcu_sched_get_gp_seq(void) { return 0; }
 static inline unsigned long rcu_exp_batches_completed(void) { return 0; }
 static inline unsigned long rcu_exp_batches_completed_sched(void) { return 0; }
 static inline unsigned long
@@ -474,19 +525,16 @@ static inline void rcu_force_quiescent_state(void) { }
 static inline void rcu_bh_force_quiescent_state(void) { }
 static inline void rcu_sched_force_quiescent_state(void) { }
 static inline void show_rcu_gp_kthreads(void) { }
+static inline int rcu_get_gp_kthreads_prio(void) { return 0; }
 #else /* #ifdef CONFIG_TINY_RCU */
-extern unsigned long rcutorture_testseq;
-extern unsigned long rcutorture_vernum;
-unsigned long rcu_batches_started(void);
-unsigned long rcu_batches_started_bh(void);
-unsigned long rcu_batches_started_sched(void);
-unsigned long rcu_batches_completed(void);
-unsigned long rcu_batches_completed_bh(void);
-unsigned long rcu_batches_completed_sched(void);
+unsigned long rcu_get_gp_seq(void);
+unsigned long rcu_bh_get_gp_seq(void);
+unsigned long rcu_sched_get_gp_seq(void);
 unsigned long rcu_exp_batches_completed(void);
 unsigned long rcu_exp_batches_completed_sched(void);
 unsigned long srcu_batches_completed(struct srcu_struct *sp);
 void show_rcu_gp_kthreads(void);
+int rcu_get_gp_kthreads_prio(void);
 void rcu_force_quiescent_state(void);
 void rcu_bh_force_quiescent_state(void);
 void rcu_sched_force_quiescent_state(void);

kernel/rcu/rcuperf.c

@@ -19,6 +19,9 @@
  *
  * Authors: Paul E. McKenney <paulmck@us.ibm.com>
  */
+
+#define pr_fmt(fmt) fmt
+
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
@@ -88,7 +91,7 @@ torture_param(int, nreaders, -1, "Number of RCU reader threads");
 torture_param(int, nwriters, -1, "Number of RCU updater threads");
 torture_param(bool, shutdown, !IS_ENABLED(MODULE),
 	      "Shutdown at end of performance tests.");
-torture_param(bool, verbose, true, "Enable verbose debugging printk()s");
+torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
 torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");
 
 static char *perf_type = "rcu";
@@ -135,8 +138,8 @@ struct rcu_perf_ops {
 	void (*cleanup)(void);
 	int (*readlock)(void);
 	void (*readunlock)(int idx);
-	unsigned long (*started)(void);
-	unsigned long (*completed)(void);
+	unsigned long (*get_gp_seq)(void);
+	unsigned long (*gp_diff)(unsigned long new, unsigned long old);
 	unsigned long (*exp_completed)(void);
 	void (*async)(struct rcu_head *head, rcu_callback_t func);
 	void (*gp_barrier)(void);
@@ -176,8 +179,8 @@ static struct rcu_perf_ops rcu_ops = {
 	.init		= rcu_sync_perf_init,
 	.readlock	= rcu_perf_read_lock,
 	.readunlock	= rcu_perf_read_unlock,
-	.started	= rcu_batches_started,
-	.completed	= rcu_batches_completed,
+	.get_gp_seq	= rcu_get_gp_seq,
+	.gp_diff	= rcu_seq_diff,
 	.exp_completed	= rcu_exp_batches_completed,
 	.async		= call_rcu,
 	.gp_barrier	= rcu_barrier,
@@ -206,8 +209,8 @@ static struct rcu_perf_ops rcu_bh_ops = {
 	.init		= rcu_sync_perf_init,
 	.readlock	= rcu_bh_perf_read_lock,
 	.readunlock	= rcu_bh_perf_read_unlock,
-	.started	= rcu_batches_started_bh,
-	.completed	= rcu_batches_completed_bh,
+	.get_gp_seq	= rcu_bh_get_gp_seq,
+	.gp_diff	= rcu_seq_diff,
 	.exp_completed	= rcu_exp_batches_completed_sched,
 	.async		= call_rcu_bh,
 	.gp_barrier	= rcu_barrier_bh,
@@ -263,8 +266,8 @@ static struct rcu_perf_ops srcu_ops = {
 	.init		= rcu_sync_perf_init,
 	.readlock	= srcu_perf_read_lock,
 	.readunlock	= srcu_perf_read_unlock,
-	.started	= NULL,
-	.completed	= srcu_perf_completed,
+	.get_gp_seq	= srcu_perf_completed,
+	.gp_diff	= rcu_seq_diff,
 	.exp_completed	= srcu_perf_completed,
 	.async		= srcu_call_rcu,
 	.gp_barrier	= srcu_rcu_barrier,
@@ -292,8 +295,8 @@ static struct rcu_perf_ops srcud_ops = {
 	.cleanup	= srcu_sync_perf_cleanup,
 	.readlock	= srcu_perf_read_lock,
 	.readunlock	= srcu_perf_read_unlock,
-	.started	= NULL,
-	.completed	= srcu_perf_completed,
+	.get_gp_seq	= srcu_perf_completed,
+	.gp_diff	= rcu_seq_diff,
 	.exp_completed	= srcu_perf_completed,
 	.async		= srcu_call_rcu,
 	.gp_barrier	= srcu_rcu_barrier,
@@ -322,8 +325,8 @@ static struct rcu_perf_ops sched_ops = {
 	.init		= rcu_sync_perf_init,
 	.readlock	= sched_perf_read_lock,
 	.readunlock	= sched_perf_read_unlock,
-	.started	= rcu_batches_started_sched,
-	.completed	= rcu_batches_completed_sched,
+	.get_gp_seq	= rcu_sched_get_gp_seq,
+	.gp_diff	= rcu_seq_diff,
 	.exp_completed	= rcu_exp_batches_completed_sched,
 	.async		= call_rcu_sched,
 	.gp_barrier	= rcu_barrier_sched,
@@ -350,8 +353,8 @@ static struct rcu_perf_ops tasks_ops = {
 	.init		= rcu_sync_perf_init,
 	.readlock	= tasks_perf_read_lock,
 	.readunlock	= tasks_perf_read_unlock,
-	.started	= rcu_no_completed,
-	.completed	= rcu_no_completed,
+	.get_gp_seq	= rcu_no_completed,
+	.gp_diff	= rcu_seq_diff,
 	.async		= call_rcu_tasks,
 	.gp_barrier	= rcu_barrier_tasks,
 	.sync		= synchronize_rcu_tasks,
@@ -359,9 +362,11 @@ static struct rcu_perf_ops tasks_ops = {
 	.name		= "tasks"
 };
 
-static bool __maybe_unused torturing_tasks(void)
+static unsigned long rcuperf_seq_diff(unsigned long new, unsigned long old)
 {
-	return cur_ops == &tasks_ops;
+	if (!cur_ops->gp_diff)
+		return new - old;
+	return cur_ops->gp_diff(new, old);
 }
 
 /*
@@ -444,8 +449,7 @@ rcu_perf_writer(void *arg)
 			b_rcu_perf_writer_started =
 				cur_ops->exp_completed() / 2;
 		} else {
-			b_rcu_perf_writer_started =
-				cur_ops->completed();
+			b_rcu_perf_writer_started = cur_ops->get_gp_seq();
 		}
 	}
 
@@ -502,7 +506,7 @@ rcu_perf_writer(void *arg)
 						cur_ops->exp_completed() / 2;
 				} else {
 					b_rcu_perf_writer_finished =
-						cur_ops->completed();
+						cur_ops->get_gp_seq();
 				}
 				if (shutdown) {
 					smp_mb(); /* Assign before wake. */
@@ -527,7 +531,7 @@ rcu_perf_writer(void *arg)
 	return 0;
 }
 
-static inline void
+static void
 rcu_perf_print_module_parms(struct rcu_perf_ops *cur_ops, const char *tag)
 {
 	pr_alert("%s" PERF_FLAG
@@ -582,8 +586,8 @@ rcu_perf_cleanup(void)
 			 t_rcu_perf_writer_finished -
 			 t_rcu_perf_writer_started,
 			 ngps,
-			 b_rcu_perf_writer_finished -
-			 b_rcu_perf_writer_started);
+			 rcuperf_seq_diff(b_rcu_perf_writer_finished,
+					  b_rcu_perf_writer_started));
 		for (i = 0; i < nrealwriters; i++) {
 			if (!writer_durations)
 				break;
@@ -671,12 +675,11 @@ rcu_perf_init(void)
 			break;
 	}
 	if (i == ARRAY_SIZE(perf_ops)) {
-		pr_alert("rcu-perf: invalid perf type: \"%s\"\n",
-			 perf_type);
+		pr_alert("rcu-perf: invalid perf type: \"%s\"\n", perf_type);
 		pr_alert("rcu-perf types:");
 		for (i = 0; i < ARRAY_SIZE(perf_ops); i++)
-			pr_alert(" %s", perf_ops[i]->name);
-		pr_alert("\n");
+			pr_cont(" %s", perf_ops[i]->name);
+		pr_cont("\n");
 		firsterr = -EINVAL;
 		goto unwind;
 	}

kernel/rcu/srcutree.c

@@ -26,6 +26,8 @@
  *
  */
 
+#define pr_fmt(fmt) "rcu: " fmt
+
 #include <linux/export.h>
 #include <linux/mutex.h>
 #include <linux/percpu.h>
@@ -390,7 +392,8 @@ void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
 		}
 	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
 	    WARN_ON(srcu_readers_active(sp))) {
-		pr_info("%s: Active srcu_struct %p state: %d\n", __func__, sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
+		pr_info("%s: Active srcu_struct %p state: %d\n",
+			__func__, sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
 		return; /* Caller forgot to stop doing call_srcu()? */
 	}
 	free_percpu(sp->sda);
@@ -641,6 +644,9 @@ static void srcu_funnel_exp_start(struct srcu_struct *sp, struct srcu_node *snp,
  * period s.  Losers must either ensure that their desired grace-period
  * number is recorded on at least their leaf srcu_node structure, or they
  * must take steps to invoke their own callbacks.
+ *
+ * Note that this function also does the work of srcu_funnel_exp_start(),
+ * in some cases by directly invoking it.
  */
 static void srcu_funnel_gp_start(struct srcu_struct *sp, struct srcu_data *sdp,
 				 unsigned long s, bool do_norm)
@@ -823,17 +829,17 @@ static void srcu_leak_callback(struct rcu_head *rhp)
  * more than one CPU, this means that when "func()" is invoked, each CPU
  * is guaranteed to have executed a full memory barrier since the end of
  * its last corresponding SRCU read-side critical section whose beginning
- * preceded the call to call_rcu().  It also means that each CPU executing
+ * preceded the call to call_srcu().  It also means that each CPU executing
  * an SRCU read-side critical section that continues beyond the start of
- * "func()" must have executed a memory barrier after the call_rcu()
+ * "func()" must have executed a memory barrier after the call_srcu()
  * but before the beginning of that SRCU read-side critical section.
  * Note that these guarantees include CPUs that are offline, idle, or
  * executing in user mode, as well as CPUs that are executing in the kernel.
  *
- * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * Furthermore, if CPU A invoked call_srcu() and CPU B invoked the
  * resulting SRCU callback function "func()", then both CPU A and CPU
  * B are guaranteed to execute a full memory barrier during the time
- * interval between the call to call_rcu() and the invocation of "func()".
+ * interval between the call to call_srcu() and the invocation of "func()".
  * This guarantee applies even if CPU A and CPU B are the same CPU (but
  * again only if the system has more than one CPU).
  *
@@ -1246,13 +1252,12 @@ static void process_srcu(struct work_struct *work)
 
 void srcutorture_get_gp_data(enum rcutorture_type test_type,
 			     struct srcu_struct *sp, int *flags,
-			     unsigned long *gpnum, unsigned long *completed)
+			     unsigned long *gp_seq)
 {
 	if (test_type != SRCU_FLAVOR)
 		return;
 	*flags = 0;
-	*completed = rcu_seq_ctr(sp->srcu_gp_seq);
-	*gpnum = rcu_seq_ctr(sp->srcu_gp_seq_needed);
+	*gp_seq = rcu_seq_current(&sp->srcu_gp_seq);
 }
 EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
 
@@ -1263,16 +1268,17 @@ void srcu_torture_stats_print(struct srcu_struct *sp, char *tt, char *tf)
 	unsigned long s0 = 0, s1 = 0;
 
 	idx = sp->srcu_idx & 0x1;
-	pr_alert("%s%s Tree SRCU per-CPU(idx=%d):", tt, tf, idx);
+	pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):",
+		 tt, tf, rcu_seq_current(&sp->srcu_gp_seq), idx);
 	for_each_possible_cpu(cpu) {
 		unsigned long l0, l1;
 		unsigned long u0, u1;
 		long c0, c1;
-		struct srcu_data *counts;
+		struct srcu_data *sdp;
 
-		counts = per_cpu_ptr(sp->sda, cpu);
-		u0 = counts->srcu_unlock_count[!idx];
-		u1 = counts->srcu_unlock_count[idx];
+		sdp = per_cpu_ptr(sp->sda, cpu);
+		u0 = sdp->srcu_unlock_count[!idx];
+		u1 = sdp->srcu_unlock_count[idx];
 
 		/*
 		 * Make sure that a lock is always counted if the corresponding
@@ -1280,12 +1286,13 @@ void srcu_torture_stats_print(struct srcu_struct *sp, char *tt, char *tf)
 		 */
 		smp_rmb();
 
-		l0 = counts->srcu_lock_count[!idx];
-		l1 = counts->srcu_lock_count[idx];
+		l0 = sdp->srcu_lock_count[!idx];
+		l1 = sdp->srcu_lock_count[idx];
 
 		c0 = l0 - u0;
 		c1 = l1 - u1;
-		pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
+		pr_cont(" %d(%ld,%ld %1p)",
+			cpu, c0, c1, rcu_segcblist_head(&sdp->srcu_cblist));
 		s0 += c0;
 		s1 += c1;
 	}

kernel/rcu/tiny.c

@@ -122,10 +122,8 @@ void rcu_check_callbacks(int user)
 {
 	if (user)
 		rcu_sched_qs();
-	else if (!in_softirq())
+	if (user || !in_softirq())
 		rcu_bh_qs();
-	if (user)
-		rcu_note_voluntary_context_switch(current);
 }
 
 /*

kernel/rcu/tree.h

@@ -81,18 +81,16 @@ struct rcu_node {
 	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
 					/*  some rcu_state fields as well as */
 					/*  following. */
-	unsigned long gpnum;	/* Current grace period for this node. */
-				/*  This will either be equal to or one */
-				/*  behind the root rcu_node's gpnum. */
-	unsigned long completed; /* Last GP completed for this node. */
-				/*  This will either be equal to or one */
-				/*  behind the root rcu_node's gpnum. */
+	unsigned long gp_seq;	/* Track rsp->rcu_gp_seq. */
+	unsigned long gp_seq_needed; /* Track rsp->rcu_gp_seq_needed. */
+	unsigned long completedqs; /* All QSes done for this node. */
 	unsigned long qsmask;	/* CPUs or groups that need to switch in */
 				/*  order for current grace period to proceed.*/
 				/*  In leaf rcu_node, each bit corresponds to */
 				/*  an rcu_data structure, otherwise, each */
 				/*  bit corresponds to a child rcu_node */
 				/*  structure. */
+	unsigned long rcu_gp_init_mask;	/* Mask of offline CPUs at GP init. */
 	unsigned long qsmaskinit;
 				/* Per-GP initial value for qsmask. */
 				/*  Initialized from ->qsmaskinitnext at the */
@@ -158,7 +156,6 @@ struct rcu_node {
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
-	u8 need_future_gp[4];	/* Counts of upcoming GP requests. */
 	raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
 
 	spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
@@ -168,22 +165,6 @@ struct rcu_node {
 	bool exp_need_flush;	/* Need to flush workitem? */
 } ____cacheline_internodealigned_in_smp;
 
-/* Accessors for ->need_future_gp[] array. */
-#define need_future_gp_mask() \
-	(ARRAY_SIZE(((struct rcu_node *)NULL)->need_future_gp) - 1)
-#define need_future_gp_element(rnp, c) \
-	((rnp)->need_future_gp[(c) & need_future_gp_mask()])
-#define need_any_future_gp(rnp)						\
-({									\
-	int __i;							\
-	bool __nonzero = false;						\
-									\
-	for (__i = 0; __i < ARRAY_SIZE((rnp)->need_future_gp); __i++)	\
-		__nonzero = __nonzero ||				\
-			    READ_ONCE((rnp)->need_future_gp[__i]);	\
-	__nonzero;							\
-})
-
 /*
  * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
  * are indexed relative to this interval rather than the global CPU ID space.
@@ -206,16 +187,14 @@ union rcu_noqs {
 /* Per-CPU data for read-copy update. */
 struct rcu_data {
 	/* 1) quiescent-state and grace-period handling : */
-	unsigned long	completed;	/* Track rsp->completed gp number */
-					/*  in order to detect GP end. */
-	unsigned long	gpnum;		/* Highest gp number that this CPU */
-					/*  is aware of having started. */
+	unsigned long	gp_seq;		/* Track rsp->rcu_gp_seq counter. */
+	unsigned long	gp_seq_needed;	/* Track rsp->rcu_gp_seq_needed ctr. */
 	unsigned long	rcu_qs_ctr_snap;/* Snapshot of rcu_qs_ctr to check */
 					/*  for rcu_all_qs() invocations. */
 	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
 	bool		core_needs_qs;	/* Core waits for quiesc state. */
 	bool		beenonline;	/* CPU online at least once. */
-	bool		gpwrap;		/* Possible gpnum/completed wrap. */
+	bool		gpwrap;		/* Possible ->gp_seq wrap. */
 	struct rcu_node *mynode;	/* This CPU's leaf of hierarchy */
 	unsigned long grpmask;		/* Mask to apply to leaf qsmask. */
 	unsigned long	ticks_this_gp;	/* The number of scheduling-clock */
@@ -239,7 +218,6 @@ struct rcu_data {
 
 	/* 4) reasons this CPU needed to be kicked by force_quiescent_state */
 	unsigned long dynticks_fqs;	/* Kicked due to dynticks idle. */
-	unsigned long offline_fqs;	/* Kicked due to being offline. */
 	unsigned long cond_resched_completed;
 					/* Grace period that needs help */
 					/*  from cond_resched(). */
@@ -278,12 +256,16 @@ struct rcu_data {
 					/* Leader CPU takes GP-end wakeups. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 
-	/* 7) RCU CPU stall data. */
+	/* 7) Diagnostic data, including RCU CPU stall warnings. */
 	unsigned int softirq_snap;	/* Snapshot of softirq activity. */
 	/* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
 	struct irq_work rcu_iw;		/* Check for non-irq activity. */
 	bool rcu_iw_pending;		/* Is ->rcu_iw pending? */
-	unsigned long rcu_iw_gpnum;	/* ->gpnum associated with ->rcu_iw. */
+	unsigned long rcu_iw_gp_seq;	/* ->gp_seq associated with ->rcu_iw. */
+	unsigned long rcu_ofl_gp_seq;	/* ->gp_seq at last offline. */
+	short rcu_ofl_gp_flags;		/* ->gp_flags at last offline. */
+	unsigned long rcu_onl_gp_seq;	/* ->gp_seq at last online. */
+	short rcu_onl_gp_flags;		/* ->gp_flags at last online. */
 
 	int cpu;
 	struct rcu_state *rsp;
@@ -340,8 +322,7 @@ struct rcu_state {
 
 	u8	boost ____cacheline_internodealigned_in_smp;
 						/* Subject to priority boost. */
-	unsigned long gpnum;			/* Current gp number. */
-	unsigned long completed;		/* # of last completed gp. */
+	unsigned long gp_seq;			/* Grace-period sequence #. */
 	struct task_struct *gp_kthread;		/* Task for grace periods. */
 	struct swait_queue_head gp_wq;		/* Where GP task waits. */
 	short gp_flags;				/* Commands for GP task. */
@@ -373,6 +354,8 @@ struct rcu_state {
 						/*  but in jiffies. */
 	unsigned long gp_activity;		/* Time of last GP kthread */
 						/*  activity in jiffies. */
+	unsigned long gp_req_activity;		/* Time of last GP request */
+						/*  in jiffies. */
 	unsigned long jiffies_stall;		/* Time at which to check */
 						/*  for CPU stalls. */
 	unsigned long jiffies_resched;		/* Time at which to resched */
@@ -384,6 +367,10 @@ struct rcu_state {
 	const char *name;			/* Name of structure. */
 	char abbr;				/* Abbreviated name. */
 	struct list_head flavors;		/* List of RCU flavors. */
+
+	spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
+						/* Synchronize offline with */
+						/*  GP pre-initialization. */
 };
 
 /* Values for rcu_state structure's gp_flags field. */
@@ -394,16 +381,20 @@ struct rcu_state {
 #define RCU_GP_IDLE	 0	/* Initial state and no GP in progress. */
 #define RCU_GP_WAIT_GPS  1	/* Wait for grace-period start. */
 #define RCU_GP_DONE_GPS  2	/* Wait done for grace-period start. */
-#define RCU_GP_WAIT_FQS  3	/* Wait for force-quiescent-state time. */
-#define RCU_GP_DOING_FQS 4	/* Wait done for force-quiescent-state time. */
-#define RCU_GP_CLEANUP   5	/* Grace-period cleanup started. */
-#define RCU_GP_CLEANED   6	/* Grace-period cleanup complete. */
+#define RCU_GP_ONOFF     3	/* Grace-period initialization hotplug. */
+#define RCU_GP_INIT      4	/* Grace-period initialization. */
+#define RCU_GP_WAIT_FQS  5	/* Wait for force-quiescent-state time. */
+#define RCU_GP_DOING_FQS 6	/* Wait done for force-quiescent-state time. */
+#define RCU_GP_CLEANUP   7	/* Grace-period cleanup started. */
+#define RCU_GP_CLEANED   8	/* Grace-period cleanup complete. */
 
 #ifndef RCU_TREE_NONCORE
 static const char * const gp_state_names[] = {
 	"RCU_GP_IDLE",
 	"RCU_GP_WAIT_GPS",
 	"RCU_GP_DONE_GPS",
+	"RCU_GP_ONOFF",
+	"RCU_GP_INIT",
 	"RCU_GP_WAIT_FQS",
 	"RCU_GP_DOING_FQS",
 	"RCU_GP_CLEANUP",
@@ -449,10 +440,13 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 static void rcu_print_detail_task_stall(struct rcu_state *rsp);
 static int rcu_print_task_stall(struct rcu_node *rnp);
 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
-static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
+static void rcu_preempt_check_blocked_tasks(struct rcu_state *rsp,
+					    struct rcu_node *rnp);
 static void rcu_preempt_check_callbacks(void);
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 static void __init __rcu_init_preempt(void);
+static void dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp,
+			    int ncheck);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static void invoke_rcu_callbacks_kthread(void);
@@ -489,7 +483,6 @@ static void __init rcu_spawn_nocb_kthreads(void);
 #ifdef CONFIG_RCU_NOCB_CPU
 static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp);
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
-static void __maybe_unused rcu_kick_nohz_cpu(int cpu);
 static bool init_nocb_callback_list(struct rcu_data *rdp);
 static void rcu_bind_gp_kthread(void);
 static bool rcu_nohz_full_cpu(struct rcu_state *rsp);

kernel/rcu/tree_exp.h

@@ -472,6 +472,7 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
 				     smp_call_func_t func)
 {
+	int cpu;
 	struct rcu_node *rnp;
 
 	trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset"));
@@ -486,13 +487,20 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
 		rnp->rew.rew_func = func;
 		rnp->rew.rew_rsp = rsp;
 		if (!READ_ONCE(rcu_par_gp_wq) ||
-		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
-			/* No workqueues yet. */
+		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
+		    rcu_is_last_leaf_node(rsp, rnp)) {
+			/* No workqueues yet or last leaf, do direct call. */
 			sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
 			continue;
 		}
 		INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
-		queue_work_on(rnp->grplo, rcu_par_gp_wq, &rnp->rew.rew_work);
+		preempt_disable();
+		cpu = cpumask_next(rnp->grplo - 1, cpu_online_mask);
+		/* If all offline, queue the work on an unbound CPU. */
+		if (unlikely(cpu > rnp->grphi))
+			cpu = WORK_CPU_UNBOUND;
+		queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
+		preempt_enable();
 		rnp->exp_need_flush = true;
 	}
 

kernel/torture.c

@@ -20,6 +20,9 @@
  * Author: Paul E. McKenney <paulmck@us.ibm.com>
  *	Based on kernel/rcu/torture.c.
  */
+
+#define pr_fmt(fmt) fmt
+
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
@@ -53,7 +56,7 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com>");
 
 static char *torture_type;
-static bool verbose;
+static int verbose;
 
 /* Mediate rmmod and system shutdown.  Concurrent rmmod & shutdown illegal! */
 #define FULLSTOP_DONTSTOP 0	/* Normal operation. */
@@ -98,7 +101,7 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
 	if (!cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
 		return false;
 
-	if (verbose)
+	if (verbose > 1)
 		pr_alert("%s" TORTURE_FLAG
 			 "torture_onoff task: offlining %d\n",
 			 torture_type, cpu);
@@ -111,7 +114,7 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
 				 "torture_onoff task: offline %d failed: errno %d\n",
 				 torture_type, cpu, ret);
 	} else {
-		if (verbose)
+		if (verbose > 1)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_onoff task: offlined %d\n",
 				 torture_type, cpu);
@@ -147,7 +150,7 @@ bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes,
 	if (cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
 		return false;
 
-	if (verbose)
+	if (verbose > 1)
 		pr_alert("%s" TORTURE_FLAG
 			 "torture_onoff task: onlining %d\n",
 			 torture_type, cpu);
@@ -160,7 +163,7 @@ bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes,
 				 "torture_onoff task: online %d failed: errno %d\n",
 				 torture_type, cpu, ret);
 	} else {
-		if (verbose)
+		if (verbose > 1)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_onoff task: onlined %d\n",
 				 torture_type, cpu);
@@ -647,7 +650,7 @@ static void torture_stutter_cleanup(void)
  * The runnable parameter points to a flag that controls whether or not
  * the test is currently runnable.  If there is no such flag, pass in NULL.
  */
-bool torture_init_begin(char *ttype, bool v)
+bool torture_init_begin(char *ttype, int v)
 {
 	mutex_lock(&fullstop_mutex);
 	if (torture_type != NULL) {

tools/testing/selftests/rcutorture/bin/kvm-recheck-rcu.sh

@@ -70,4 +70,5 @@ else
 	else
 		print_warning $nclosecalls "Reader Batch close calls in" $(($dur/60)) minute run: $i
 	fi
+	echo $nclosecalls "Reader Batch close calls in" $(($dur/60)) minute run: $i > $i/console.log.rcu.diags
 fi

tools/testing/selftests/rcutorture/bin/kvm-recheck.sh

@@ -39,6 +39,7 @@ do
 			head -1 $resdir/log
 		fi
 		TORTURE_SUITE="`cat $i/../TORTURE_SUITE`"
+		rm -f $i/console.log.*.diags
 		kvm-recheck-${TORTURE_SUITE}.sh $i
 		if test -f "$i/console.log"
 		then

tools/testing/selftests/rcutorture/configs/rcu/TREE08-T.boot

-rcutree.rcu_fanout_exact=1