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>
This commit is contained in:
Paul E. McKenney
2009-09-23 09:50:41 -07:00
committed by Ingo Molnar
parent 0729e19614
commit fc2219d49e
4 changed files with 46 additions and 40 deletions

View File

@@ -150,6 +150,16 @@ void __rcu_read_lock(void)
}
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 @@ static void rcu_read_unlock_special(struct task_struct *t)
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 @@ static void rcu_read_unlock_special(struct task_struct *t)
* 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 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
{
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_print_task_stall(struct rcu_node *rnp)
*/
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 @@ static void rcu_preempt_note_context_switch(int cpu)
{
}
/*
* 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 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
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
/*