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rcu: Update rcu_preempt_deferred_qs() comments for !PREEMPT kernels

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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: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Zqiang 2022-06-20 14:42:24 +08:00 committed by Paul E. McKenney
parent 6d60ea03ac
commit bca4fa8cb0
1 changed files with 7 additions and 4 deletions
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11
kernel/rcu/tree_plugin.h
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@ -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);