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

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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: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-03-26 10:22:22 -07:00
parent f1a98045ab
commit add0d37b4f
2 changed files with 3 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
kernel/rcu/tree_exp.h
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@ -633,7 +633,7 @@ static void rcu_exp_handler(void *unused)
raw_spin_lock_irqsave_rcu_node(rnp, flags); raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->expmask & rdp->grpmask) { if (rnp->expmask & rdp->grpmask) {
rdp->deferred_qs = true; 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); raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return; return;

4
kernel/rcu/tree_plugin.h
View file

@ -285,7 +285,7 @@ static void rcu_qs(void)
TPS("cpuqs")); TPS("cpuqs"));
__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */ 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))) { if (unlikely(!list_empty(&current->rcu_node_entry))) {
t->rcu_read_lock_nesting = 1; t->rcu_read_lock_nesting = 1;
barrier(); 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)) { } else if (unlikely(t->rcu_read_lock_nesting)) {
t->rcu_read_lock_nesting = 1; t->rcu_read_lock_nesting = 1;
} else { } else {