[tip:core/rcu] rcu: Clean up code based on review feedback from Josh Triplett, part 4

From: tip-bot for Paul E. McKenney
Date: Mon Oct 05 2009 - 15:11:57 EST

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Commit-ID: a0b6c9a78c41dc36732d6e1e90f0f2f57b29816f
Gitweb: http://git.kernel.org/tip/a0b6c9a78c41dc36732d6e1e90f0f2f57b29816f
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 28 Sep 2009 07:46:33 -0700
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Mon, 5 Oct 2009 21:02:04 +0200

rcu: Clean up code based on review feedback from Josh Triplett, part 4

These issues identified during an old-fashioned face-to-face code
review extending over many hours. This group improves an existing
abstraction and introduces two new ones. It also fixes an RCU
stall-warning bug found while making the other changes.

o Make RCU_INIT_FLAVOR() declare its own variables, removing
the need to declare them at each call site.

o Create an rcu_for_each_leaf() macro that scans the leaf
nodes of the rcu_node tree.

o Create an rcu_for_each_node_breadth_first() macro that does
a breadth-first traversal of the rcu_node tree, AKA
stepping through the array in index-number order.

o If all CPUs corresponding to a given leaf rcu_node
structure go offline, then any tasks queued on that leaf
will be moved to the root rcu_node structure. Therefore,
the stall-warning code must dump out tasks queued on the
root rcu_node structure as well as those queued on the leaf
rcu_node structures.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: laijs@xxxxxxxxxxxxxx
Cc: dipankar@xxxxxxxxxx
Cc: akpm@xxxxxxxxxxxxxxxxxxxx
Cc: mathieu.desnoyers@xxxxxxxxxx
Cc: josh@xxxxxxxxxxxxxxxx
Cc: dvhltc@xxxxxxxxxx
Cc: niv@xxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: Valdis.Kletnieks@xxxxxx
Cc: dhowells@xxxxxxxxxx
LKML-Reference: <12541491934126-git-send-email->
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

---
kernel/rcutree.c | 53 ++++++++++++++++++++++++----------------------
kernel/rcutree.h | 12 ++++++++++
kernel/rcutree_plugin.h | 4 ---
3 files changed, 40 insertions(+), 29 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d559783..e2e272b 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -462,8 +462,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
long delta;
unsigned long flags;
struct rcu_node *rnp = rcu_get_root(rsp);
- struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
- struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];

/* Only let one CPU complain about others per time interval. */

@@ -474,18 +472,24 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
return;
}
rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
+
+ /*
+ * Now rat on any tasks that got kicked up to the root rcu_node
+ * due to CPU offlining.
+ */
+ rcu_print_task_stall(rnp);
spin_unlock_irqrestore(&rnp->lock, flags);

/* OK, time to rat on our buddy... */

printk(KERN_ERR "INFO: RCU detected CPU stalls:");
- for (; rnp_cur < rnp_end; rnp_cur++) {
+ rcu_for_each_leaf_node(rsp, rnp) {
rcu_print_task_stall(rnp);
- if (rnp_cur->qsmask == 0)
+ if (rnp->qsmask == 0)
continue;
- for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++)
- if (rnp_cur->qsmask & (1UL << cpu))
- printk(" %d", rnp_cur->grplo + cpu);
+ for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
+ if (rnp->qsmask & (1UL << cpu))
+ printk(" %d", rnp->grplo + cpu);
}
printk(" (detected by %d, t=%ld jiffies)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start));
@@ -649,7 +653,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
* one corresponding to this CPU, due to the fact that we have
* irqs disabled.
*/
- for (rnp = &rsp->node[0]; rnp < &rsp->node[NUM_RCU_NODES]; rnp++) {
+ rcu_for_each_node_breadth_first(rsp, rnp) {
spin_lock(&rnp->lock); /* irqs already disabled. */
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
@@ -1042,33 +1046,32 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
int cpu;
unsigned long flags;
unsigned long mask;
- struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
- struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];
+ struct rcu_node *rnp;

- for (; rnp_cur < rnp_end; rnp_cur++) {
+ rcu_for_each_leaf_node(rsp, rnp) {
mask = 0;
- spin_lock_irqsave(&rnp_cur->lock, flags);
+ spin_lock_irqsave(&rnp->lock, flags);
if (rsp->completed != lastcomp) {
- spin_unlock_irqrestore(&rnp_cur->lock, flags);
+ spin_unlock_irqrestore(&rnp->lock, flags);
return 1;
}
- if (rnp_cur->qsmask == 0) {
- spin_unlock_irqrestore(&rnp_cur->lock, flags);
+ if (rnp->qsmask == 0) {
+ spin_unlock_irqrestore(&rnp->lock, flags);
continue;
}
- cpu = rnp_cur->grplo;
+ cpu = rnp->grplo;
bit = 1;
- for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) {
- if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu]))
+ for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
+ if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
mask |= bit;
}
if (mask != 0 && rsp->completed == lastcomp) {

- /* cpu_quiet_msk() releases rnp_cur->lock. */
- cpu_quiet_msk(mask, rsp, rnp_cur, flags);
+ /* cpu_quiet_msk() releases rnp->lock. */
+ cpu_quiet_msk(mask, rsp, rnp, flags);
continue;
}
- spin_unlock_irqrestore(&rnp_cur->lock, flags);
+ spin_unlock_irqrestore(&rnp->lock, flags);
}
return 0;
}
@@ -1550,6 +1553,10 @@ static void __init rcu_init_one(struct rcu_state *rsp)
*/
#define RCU_INIT_FLAVOR(rsp, rcu_data) \
do { \
+ int i; \
+ int j; \
+ struct rcu_node *rnp; \
+ \
rcu_init_one(rsp); \
rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
j = 0; \
@@ -1564,10 +1571,6 @@ do { \

void __init __rcu_init(void)
{
- int i; /* All used by RCU_INIT_FLAVOR(). */
- int j;
- struct rcu_node *rnp;
-
rcu_bootup_announce();
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index e6ab31c..676eecd 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -106,6 +106,18 @@ struct rcu_node {
/* blocked_tasks[] array. */
} ____cacheline_internodealigned_in_smp;

+/*
+ * Do a full breadth-first scan of the rcu_node structures for the
+ * specified rcu_state structure.
+ */
+#define rcu_for_each_node_breadth_first(rsp, rnp) \
+ for ((rnp) = &(rsp)->node[0]; \
+ (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
+
+#define rcu_for_each_leaf_node(rsp, rnp) \
+ for ((rnp) = (rsp)->level[NUM_RCU_LVLS - 1]; \
+ (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++)
+
/* Index values for nxttail array in struct rcu_data. */
#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 6525021..57200fe 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -423,10 +423,6 @@ static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
*/
static void __init __rcu_init_preempt(void)
{
- int i; /* All used by RCU_INIT_FLAVOR(). */
- int j;
- struct rcu_node *rnp;
-
RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
}

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Next message: tip-bot for Paul E. McKenney: "[tip:core/rcu] rcu: Move rcu_barrier() to rcutree, make lightweight rcu_barrier() for rcutiny"
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