Merge tag 'rcu.6.4.april5.2023.3' of git://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux

Pull RCU updates from Joel Fernandes:

 - Updates and additions to MAINTAINERS files, with Boqun being added to
   the RCU entry and Zqiang being added as an RCU reviewer.

   I have also transitioned from reviewer to maintainer; however, Paul
   will be taking over sending RCU pull-requests for the next merge
   window.

 - Resolution of hotplug warning in nohz code, achieved by fixing
   cpu_is_hotpluggable() through interaction with the nohz subsystem.

   Tick dependency modifications by Zqiang, focusing on fixing usage of
   the TICK_DEP_BIT_RCU_EXP bitmask.

 - Avoid needless calls to the rcu-lazy shrinker for CONFIG_RCU_LAZY=n
   kernels, fixed by Zqiang.

 - Improvements to rcu-tasks stall reporting by Neeraj.

 - Initial renaming of k[v]free_rcu() to k[v]free_rcu_mightsleep() for
   increased robustness, affecting several components like mac802154,
   drbd, vmw_vmci, tracing, and more.

   A report by Eric Dumazet showed that the API could be unknowingly
   used in an atomic context, so we'd rather make sure they know what
   they're asking for by being explicit:

      https://lore.kernel.org/all/20221202052847.2623997-1-edumazet@google.com/

 - Documentation updates, including corrections to spelling,
   clarifications in comments, and improvements to the srcu_size_state
   comments.

 - Better srcu_struct cache locality for readers, by adjusting the size
   of srcu_struct in support of SRCU usage by Christoph Hellwig.

 - Teach lockdep to detect deadlocks between srcu_read_lock() vs
   synchronize_srcu() contributed by Boqun.

   Previously lockdep could not detect such deadlocks, now it can.

 - Integration of rcutorture and rcu-related tools, targeted for v6.4
   from Boqun's tree, featuring new SRCU deadlock scenarios, test_nmis
   module parameter, and more

 - Miscellaneous changes, various code cleanups and comment improvements

* tag 'rcu.6.4.april5.2023.3' of git://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux: (71 commits)
  checkpatch: Error out if deprecated RCU API used
  mac802154: Rename kfree_rcu() to kvfree_rcu_mightsleep()
  rcuscale: Rename kfree_rcu() to kfree_rcu_mightsleep()
  ext4/super: Rename kfree_rcu() to kfree_rcu_mightsleep()
  net/mlx5: Rename kfree_rcu() to kfree_rcu_mightsleep()
  net/sysctl: Rename kvfree_rcu() to kvfree_rcu_mightsleep()
  lib/test_vmalloc.c: Rename kvfree_rcu() to kvfree_rcu_mightsleep()
  tracing: Rename kvfree_rcu() to kvfree_rcu_mightsleep()
  misc: vmw_vmci: Rename kvfree_rcu() to kvfree_rcu_mightsleep()
  drbd: Rename kvfree_rcu() to kvfree_rcu_mightsleep()
  rcu: Protect rcu_print_task_exp_stall() ->exp_tasks access
  rcu: Avoid stack overflow due to __rcu_irq_enter_check_tick() being kprobe-ed
  rcu-tasks: Report stalls during synchronize_srcu() in rcu_tasks_postscan()
  rcu: Permit start_poll_synchronize_rcu_expedited() to be invoked early
  rcu: Remove never-set needwake assignment from rcu_report_qs_rdp()
  rcu: Register rcu-lazy shrinker only for CONFIG_RCU_LAZY=y kernels
  rcu: Fix missing TICK_DEP_MASK_RCU_EXP dependency check
  rcu: Fix set/clear TICK_DEP_BIT_RCU_EXP bitmask race
  rcu/trace: use strscpy() to instead of strncpy()
  tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem
  ...

1 files changed, 41 insertions, 2 deletions

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 115616ac3bfa..4a1b9622598b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -14,6 +14,43 @@
 
 /*
  * Grace-period counter management.
+ *
+ * The two least significant bits contain the control flags.
+ * The most significant bits contain the grace-period sequence counter.
+ *
+ * When both control flags are zero, no grace period is in progress.
+ * When either bit is non-zero, a grace period has started and is in
+ * progress. When the grace period completes, the control flags are reset
+ * to 0 and the grace-period sequence counter is incremented.
+ *
+ * However some specific RCU usages make use of custom values.
+ *
+ * SRCU special control values:
+ *
+ *	SRCU_SNP_INIT_SEQ	:	Invalid/init value set when SRCU node
+ *					is initialized.
+ *
+ *	SRCU_STATE_IDLE		:	No SRCU gp is in progress
+ *
+ *	SRCU_STATE_SCAN1	:	State set by rcu_seq_start(). Indicates
+ *					we are scanning the readers on the slot
+ *					defined as inactive (there might well
+ *					be pending readers that will use that
+ *					index, but their number is bounded).
+ *
+ *	SRCU_STATE_SCAN2	:	State set manually via rcu_seq_set_state()
+ *					Indicates we are flipping the readers
+ *					index and then scanning the readers on the
+ *					slot newly designated as inactive (again,
+ *					the number of pending readers that will use
+ *					this inactive index is bounded).
+ *
+ * RCU polled GP special control value:
+ *
+ *	RCU_GET_STATE_COMPLETED :	State value indicating an already-completed
+ *					polled GP has completed.  This value covers
+ *					both the state and the counter of the
+ *					grace-period sequence number.
  */
 
 #define RCU_SEQ_CTR_SHIFT	2
@@ -341,11 +378,13 @@ extern void rcu_init_geometry(void);
  * specified state structure (for SRCU) or the only rcu_state structure
  * (for RCU).
  */
-#define srcu_for_each_node_breadth_first(sp, rnp) \
+#define _rcu_for_each_node_breadth_first(sp, rnp) \
 	for ((rnp) = &(sp)->node[0]; \
 	     (rnp) < &(sp)->node[rcu_num_nodes]; (rnp)++)
 #define rcu_for_each_node_breadth_first(rnp) \
-	srcu_for_each_node_breadth_first(&rcu_state, rnp)
+	_rcu_for_each_node_breadth_first(&rcu_state, rnp)
+#define srcu_for_each_node_breadth_first(ssp, rnp) \
+	_rcu_for_each_node_breadth_first(ssp->srcu_sup, rnp)
 
 /*
  * Scan the leaves of the rcu_node hierarchy for the rcu_state structure.