rcu: Clean up code based on review feedback from Josh Triplett
These issues identified during an old-fashioned face-to-face code
review extended over many hours.
o Bury various forms of the "rsp->completed == rsp->gpnum"
comparison into an rcu_gp_in_progress() function, which has
the beneficial side-effect of forcing consistent use of
ACCESS_ONCE().
o Replace hand-coded arithmetic with DIV_ROUND_UP().
o Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])"
instances into an rcu_preempted_readers() function, as this
expression indicates that there are no readers blocked
within RCU read-side critical sections blocking the current
grace period. (Though there might well be similar readers
blocking the next grace period.)
o Remove a dangling rcu_restart_cpu() declaration that has
been dangling for almost 20 minor releases of the kernel.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12537246442687-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 1cee04f..8ff1ba7 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -150,6 +150,16 @@
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
+/*
+ * Check for preempted RCU readers blocking the current grace period
+ * for the specified rcu_node structure. If the caller needs a reliable
+ * answer, it must hold the rcu_node's ->lock.
+ */
+static int rcu_preempted_readers(struct rcu_node *rnp)
+{
+ return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
+}
+
static void rcu_read_unlock_special(struct task_struct *t)
{
int empty;
@@ -196,7 +206,7 @@
break;
spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
- empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
+ empty = !rcu_preempted_readers(rnp);
list_del_init(&t->rcu_node_entry);
t->rcu_blocked_node = NULL;
@@ -207,7 +217,7 @@
* drop rnp->lock and restore irq.
*/
if (!empty && rnp->qsmask == 0 &&
- list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])) {
+ !rcu_preempted_readers(rnp)) {
struct rcu_node *rnp_p;
if (rnp->parent == NULL) {
@@ -257,12 +267,12 @@
{
unsigned long flags;
struct list_head *lp;
- int phase = rnp->gpnum & 0x1;
+ int phase;
struct task_struct *t;
- if (!list_empty(&rnp->blocked_tasks[phase])) {
+ if (rcu_preempted_readers(rnp)) {
spin_lock_irqsave(&rnp->lock, flags);
- phase = rnp->gpnum & 0x1; /* re-read under lock. */
+ phase = rnp->gpnum & 0x1;
lp = &rnp->blocked_tasks[phase];
list_for_each_entry(t, lp, rcu_node_entry)
printk(" P%d", t->pid);
@@ -281,20 +291,10 @@
*/
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
- WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]));
+ WARN_ON_ONCE(rcu_preempted_readers(rnp));
WARN_ON_ONCE(rnp->qsmask);
}
-/*
- * Check for preempted RCU readers for the specified rcu_node structure.
- * If the caller needs a reliable answer, it must hold the rcu_node's
- * >lock.
- */
-static int rcu_preempted_readers(struct rcu_node *rnp)
-{
- return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
-}
-
#ifdef CONFIG_HOTPLUG_CPU
/*
@@ -461,6 +461,15 @@
{
}
+/*
+ * Because preemptable RCU does not exist, there are never any preempted
+ * RCU readers.
+ */
+static int rcu_preempted_readers(struct rcu_node *rnp)
+{
+ return 0;
+}
+
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
/*
@@ -483,15 +492,6 @@
WARN_ON_ONCE(rnp->qsmask);
}
-/*
- * Because preemptable RCU does not exist, there are never any preempted
- * RCU readers.
- */
-static int rcu_preempted_readers(struct rcu_node *rnp)
-{
- return 0;
-}
-
#ifdef CONFIG_HOTPLUG_CPU
/*