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rcu: Clarify and correct the rcu_preempt_qs() header comment 

The rcu_preempt_qs() function only applies to the CPU, not the task.
A task really is allowed to invoke this function while in an RCU-preempt
read-side critical section, but only if it has first added itself to
some leaf rcu_node structure's ->blkd_tasks list.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-05-16 18:00:17 -07:00
parent 3b57a3994f
commit c7037ff524
1 changed files with 10 additions and 6 deletions
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16
kernel/rcu/tree_plugin.h
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@ -294,13 +294,17 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
}
/*
* Record a preemptible-RCU quiescent state for the specified CPU. Note
* that this just means that the task currently running on the CPU is
* not in a quiescent state. There might be any number of tasks blocked
* while in an RCU read-side critical section.
* Record a preemptible-RCU quiescent state for the specified CPU.
* Note that this does not necessarily mean that the task currently running
* on the CPU is in a quiescent state: Instead, it means that the current
* grace period need not wait on any RCU read-side critical section that
* starts later on this CPU. It also means that if the current task is
* in an RCU read-side critical section, it has already added itself to
* some leaf rcu_node structure's ->blkd_tasks list. In addition to the
* current task, there might be any number of other tasks blocked while
* in an RCU read-side critical section.
*
* As with the other rcu_*_qs() functions, callers to this function
* must disable preemption.
* Callers to this function must disable preemption.
*/
static void rcu_preempt_qs(void)
{