Commit bca4fa8c authored by Zqiang's avatar Zqiang Committed by Paul E. McKenney
Browse files

rcu: Update rcu_preempt_deferred_qs() comments for !PREEMPT kernels 



In non-premptible kernels, tasks never do context switches within
RCU read-side critical sections.  Therefore, in such kernels, each
leaf rcu_node structure's ->blkd_tasks list will always be empty.
The comment on the non-preemptible version of rcu_preempt_deferred_qs()
confuses this point, so this commit therefore fixes it.

Signed-off-by: default avatarZqiang <qiang1.zhang@intel.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 6d60ea03

kernel/rcu/tree_plugin.h

+7 −4
Original line number Diff line number Diff line
@@ -932,10 +932,13 @@ static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) 
	return false;

}



// Except that we do need to respond to a request by an expedited grace

// period for a quiescent state from this CPU.  Note that requests from

// tasks are handled when removing the task from the blocked-tasks list

// below.

// Except that we do need to respond to a request by an expedited

// grace period for a quiescent state from this CPU.  Note that in

// non-preemptible kernels, there can be no context switches within RCU

// read-side critical sections, which in turn means that the leaf rcu_node

// structure's blocked-tasks list is always empty.  is therefore no need to

// actually check it.  Instead, a quiescent state from this CPU suffices,

// and this function is only called from such a quiescent state.

notrace void rcu_preempt_deferred_qs(struct task_struct *t)

{

	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);