Commit 45f4b4a2 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu-tasks: Add comments explaining task_struct strategy 



Accesses to task_struct structures must be either protected by RCU
or by get_task_struct().  Tasks trace RCU uses these in a non-obvious
combination, in conjunction with an IPI handler.  This commit therefore
adds comments explaining this usage.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 2734d6c1

kernel/rcu/tasks.h

+10 −1
Original line number Diff line number Diff line
@@ -785,7 +785,10 @@ EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); 
//	set that task's .need_qs flag so that task's next outermost

//	rcu_read_unlock_trace() will report the quiescent state (in which

//	case the count of readers is incremented).  If both attempts fail,

//	the task is added to a "holdout" list.

//	the task is added to a "holdout" list.  Note that IPIs are used

//	to invoke trc_read_check_handler() in the context of running tasks

//	in order to avoid ordering overhead on common-case shared-variable

//	accessses.

// rcu_tasks_trace_postscan():

//	Initialize state and attempt to identify an immediate quiescent

//	state as above (but only for idle tasks), unblock CPU-hotplug
@@ -994,6 +997,12 @@ static void trc_wait_for_one_reader(struct task_struct *t, 
	}

	put_task_struct(t);



	// If this task is not yet on the holdout list, then we are in

	// an RCU read-side critical section.  Otherwise, the invocation of

	// rcu_add_holdout() that added it to the list did the necessary

	// get_task_struct().  Either way, the task cannot be freed out

	// from under this code.



	// If currently running, send an IPI, either way, add to list.

	trc_add_holdout(t, bhp);

	if (task_curr(t) &&