Merge tag 'rcu.release.v7.2' of gitolite.kernel.org:pub/scm/linux/kernel/git/rcu/linux

Pull RCU updates from Uladzislau Rezki:
 "Torture test updates:

   - Improve kvm-series.sh script by adding examples in its header
     comment

   - Lazy RCU is more fully tested now by replacing call_rcu_hurry()
     with call_rcu() and doing rcu_barrier() to motivate lazy callbacks
     during a stutter pause

   - Add more synonyms for the "--do-normal" group of torture.sh
     command-line arguments

  Misc changes:

   - Reduce stack usage of nocb_gp_wait() to address frame size warning
     when built with CONFIG_UBSAN_ALIGNMENT

   - The synchronize_rcu() call can detect the flood and latches a
     normal/default path temporary switching to wait_rcu_gp() path

   - Document using rcu_access_pointer() to fetch the old pointer for
     lockless cmpxchg() updates

   - Simplify some RCU code using clamp_val()

   - Fix a kerneldoc header comment typo in srcu_down_read_fast()"

* tag 'rcu.release.v7.2' of gitolite.kernel.org:pub/scm/linux/kernel/git/rcu/linux:
  rcu/nocb: reduce stack usage in nocb_gp_wait()
  rcu-tasks: Fix possible boot-time tests failed for the call_rcu_tasks()
  rcu: Latch normal synchronize_rcu() path on flood
  rcu: Document rcu_access_pointer() feeding into cmpxchg()
  rcu: Simplify param_set_next_fqs_jiffies() by applying clamp_val()
  rcu: Simplify rcu_do_batch() by applying clamp()
  checkpatch: Undeprecate rcu_read_lock_trace() and rcu_read_unlock_trace()
  srcu: Fix kerneldoc header comment typo in srcu_down_read_fast()
  torture: Allow "norm" abbreviation for "normal"
  torture: Improve kvm-series.sh header comment
  torture: Add torture_sched_set_normal() for user-specified nice values
  rcutorture: Fully test lazy RCU

3 files changed, 9 insertions, 6 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index bfa765132de8..5e95acc33989 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -592,11 +592,13 @@ context_unsafe(							      \
  * lockdep checks for being in an RCU read-side critical section.  This is
  * useful when the value of this pointer is accessed, but the pointer is
  * not dereferenced, for example, when testing an RCU-protected pointer
- * against NULL.  Although rcu_access_pointer() may also be used in cases
- * where update-side locks prevent the value of the pointer from changing,
- * you should instead use rcu_dereference_protected() for this use case.
- * Within an RCU read-side critical section, there is little reason to
- * use rcu_access_pointer().
+ * against NULL.  Within an RCU read-side critical section, there is little
+ * reason to use rcu_access_pointer().  Although rcu_access_pointer() may
+ * also be used in cases where update-side locks prevent the value of the
+ * pointer from changing, you should instead use rcu_dereference_protected()
+ * for this use case.  It is also permissible to use rcu_access_pointer()
+ * within lockless updaters to obtain the old value for an atomic operation,
+ * for example, for cmpxchg().
  *
  * It is usually best to test the rcu_access_pointer() return value
  * directly in order to avoid accidental dereferences being introduced
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 81b1938512d5..a54ce9e808b9 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -397,7 +397,7 @@ static inline struct srcu_ctr __percpu *srcu_read_lock_fast_notrace(struct srcu_
  *
  * The same srcu_struct may be used concurrently by srcu_down_read_fast()
  * and srcu_read_lock_fast().  However, the same definition/initialization
- * requirements called out for srcu_read_lock_safe() apply.
+ * requirements called out for srcu_read_lock_fast_updown() apply.
  */
 static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *ssp) __acquires_shared(ssp)
 {
diff --git a/include/linux/torture.h b/include/linux/torture.h
index 1b59056c3b18..c9b47d138302 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -129,6 +129,7 @@ void _torture_stop_kthread(char *m, struct task_struct **tp);
 #else
 #define torture_preempt_schedule()	do { } while (0)
 #endif
+void torture_sched_set_normal(struct task_struct *t, int nice);
 
 #if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_MODULE(CONFIG_LOCK_TORTURE_TEST)
 long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask, bool dowarn);