Commit add0d37b authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Correct READ_ONCE()/WRITE_ONCE() for ->rcu_read_unlock_special 



The task_struct structure's ->rcu_read_unlock_special field is only ever
read or written by the owning task, but it is accessed both at process
and interrupt levels.  It may therefore be accessed using plain reads
and writes while interrupts are disabled, but must be accessed using
READ_ONCE() and WRITE_ONCE() or better otherwise.  This commit makes a
few adjustments to align with this discipline.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent f1a98045

kernel/rcu/tree_exp.h

+1 −1
Original line number Diff line number Diff line
@@ -633,7 +633,7 @@ static void rcu_exp_handler(void *unused) 
		raw_spin_lock_irqsave_rcu_node(rnp, flags);

		if (rnp->expmask & rdp->grpmask) {

			rdp->deferred_qs = true;

			WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, true);

			t->rcu_read_unlock_special.b.exp_hint = true;

		}

		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

		return;

kernel/rcu/tree_plugin.h

+2 −2
Original line number Diff line number Diff line
@@ -285,7 +285,7 @@ static void rcu_qs(void) 
				       TPS("cpuqs"));

		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);

		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */

		current->rcu_read_unlock_special.b.need_qs = false;

		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);

	}

}
@@ -817,7 +817,7 @@ void exit_rcu(void) 
	if (unlikely(!list_empty(&current->rcu_node_entry))) {

		t->rcu_read_lock_nesting = 1;

		barrier();

		t->rcu_read_unlock_special.b.blocked = true;

		WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);

	} else if (unlikely(t->rcu_read_lock_nesting)) {

		t->rcu_read_lock_nesting = 1;

	} else {

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