doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()

Now that cond_resched() also provides RCU quiescent states when
needed, it can be used in place of cond_resched_rcu_qs().  This
commit therefore documents this change.

Signed-off-by: Paul E. McKenney <[email protected]>

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

@@ -1097,7 +1097,8 @@ <h5>Quiescent-State and Grace-Period Tracking</h5>
 its next exit from idle.
 Finally, the <tt>rcu_qs_ctr_snap</tt> field is used to detect
 cases where a given operation has resulted in a quiescent state
-for all flavors of RCU, for example, <tt>cond_resched_rcu_qs()</tt>.
+for all flavors of RCU, for example, <tt>cond_resched()</tt>
+when RCU has indicated a need for quiescent states.
 
 <h5>RCU Callback Handling</h5>
 

Documentation/RCU/Design/Requirements/Requirements.html

@@ -2797,7 +2797,7 @@ <h3><a name="Performance, Scalability, Response Time, and Reliability">
 executing in usermode (which is one use case for
 <tt>CONFIG_NO_HZ_FULL=y</tt>) or in the kernel.
 That said, CPU-bound loops in the kernel must execute
-<tt>cond_resched_rcu_qs()</tt> at least once per few tens of milliseconds
+<tt>cond_resched()</tt> at least once per few tens of milliseconds
 in order to avoid receiving an IPI from RCU.
 
 <p>
@@ -3128,7 +3128,7 @@ <h3><a name="Tasks RCU">Tasks RCU</a></h3>
 is to have implicit
 read-side critical sections that are delimited by voluntary context
 switches, that is, calls to <tt>schedule()</tt>,
-<tt>cond_resched_rcu_qs()</tt>, and
+<tt>cond_resched()</tt>, and
 <tt>synchronize_rcu_tasks()</tt>.
 In addition, transitions to and from userspace execution also delimit
 tasks-RCU read-side critical sections.

Documentation/RCU/stallwarn.txt

@@ -23,12 +23,10 @@ o	A CPU looping with preemption disabled.  This condition can
 o	A CPU looping with bottom halves disabled.  This condition can
 	result in RCU-sched and RCU-bh stalls.
 
-o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the
-	kernel without invoking schedule().  Note that cond_resched()
-	does not necessarily prevent RCU CPU stall warnings.  Therefore,
-	if the looping in the kernel is really expected and desirable
-	behavior, you might need to replace some of the cond_resched()
-	calls with calls to cond_resched_rcu_qs().
+o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
+	without invoking schedule().  If the looping in the kernel is
+	really expected and desirable behavior, you might need to add
+	some calls to cond_resched().
 
 o	Booting Linux using a console connection that is too slow to
 	keep up with the boot-time console-message rate.  For example,