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Date: Wed, 5 Nov 2014 09:41:28 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
bobby.prani@...il.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/10] rcu: Abstract rcu_cleanup_dead_rnp() from rcu_cleanup_dead_cpu()
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
This commit abstracts rcu_cleanup_dead_rnp() from rcu_cleanup_dead_cpu()
in preparation for the rework of RCU priority boosting. This new function
will be invoked from rcu_read_unlock_special() in the reworked scheme,
which is why rcu_cleanup_dead_rnp() assumes that the leaf rcu_node
structure's ->qsmaskinit field has already been updated.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 67 ++++++++++++++++++++++++++++++++++--------------
kernel/rcu/tree.h | 1 +
kernel/rcu/tree_plugin.h | 17 ++++++++++++
3 files changed, 66 insertions(+), 19 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1b8dc3f8d80c..ccaf5ec78a56 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2195,6 +2195,46 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
}
/*
+ * All CPUs for the specified rcu_node structure have gone offline,
+ * and all tasks that were preempted within an RCU read-side critical
+ * section while running on one of those CPUs have since exited their RCU
+ * read-side critical section. Some other CPU is reporting this fact with
+ * the specified rcu_node structure's ->lock held and interrupts disabled.
+ * This function therefore goes up the tree of rcu_node structures,
+ * clearing the corresponding bits in the ->qsmaskinit fields. Note that
+ * the leaf rcu_node structure's ->qsmaskinit field has already been
+ * updated
+ *
+ * This function does check that the specified rcu_node structure has
+ * all CPUs offline and no blocked tasks, so it is OK to invoke it
+ * prematurely. That said, invoking it after the fact will cost you
+ * a needless lock acquisition. So once it has done its work, don't
+ * invoke it again.
+ */
+static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
+{
+ long mask;
+ struct rcu_node *rnp = rnp_leaf;
+
+ if (rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
+ return;
+ for (;;) {
+ mask = rnp->grpmask;
+ rnp = rnp->parent;
+ if (!rnp)
+ break;
+ raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ smp_mb__after_unlock_lock(); /* GP memory ordering. */
+ rnp->qsmaskinit &= ~mask;
+ if (rnp->qsmaskinit) {
+ raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ return;
+ }
+ raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+ }
+}
+
+/*
* The CPU has been completely removed, and some other CPU is reporting
* this fact from process context. Do the remainder of the cleanup,
* including orphaning the outgoing CPU's RCU callbacks, and also
@@ -2204,7 +2244,6 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
- unsigned long mask;
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
@@ -2220,24 +2259,14 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
rcu_adopt_orphan_cbs(rsp, flags);
- /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
- mask = rdp->grpmask; /* rnp->grplo is constant. */
- do {
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
- smp_mb__after_unlock_lock();
- rnp->qsmaskinit &= ~mask;
- if (rnp->qsmaskinit != 0) {
- if (rnp != rdp->mynode)
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- break;
- }
- if (rnp == rdp->mynode)
- need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
- else
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
- mask = rnp->grpmask;
- rnp = rnp->parent;
- } while (rnp != NULL);
+ /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
+ raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ smp_mb__after_unlock_lock(); /* Enforce GP memory-order guarantee. */
+ rnp->qsmaskinit &= ~rdp->grpmask;
+ if (rnp->qsmaskinit == 0) {
+ need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
+ rcu_cleanup_dead_rnp(rnp);
+ }
/*
* We still hold the leaf rcu_node structure lock here, and
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 8e7b1843896e..bdf53aabaf42 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -553,6 +553,7 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
unsigned long flags);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
static void rcu_print_detail_task_stall(struct rcu_state *rsp);
static int rcu_print_task_stall(struct rcu_node *rnp);
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 3d22f0b2dea9..10d934cab9b3 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -307,6 +307,15 @@ static struct list_head *rcu_next_node_entry(struct task_struct *t,
}
/*
+ * Return true if the specified rcu_node structure has tasks that were
+ * preempted within an RCU read-side critical section.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
+{
+ return !list_empty(&rnp->blkd_tasks);
+}
+
+/*
* Handle special cases during rcu_read_unlock(), such as needing to
* notify RCU core processing or task having blocked during the RCU
* read-side critical section.
@@ -970,6 +979,14 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
+ * Because there is no preemptible RCU, there can be no readers blocked.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
+{
+ return false;
+}
+
+/*
* Because preemptible RCU does not exist, we never have to check for
* tasks blocked within RCU read-side critical sections.
*/
--
1.8.1.5
--
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