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Date: Wed, 23 Sep 2009 19:13:11 GMT
From: "tip-bot for Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
hpa@...or.com, mingo@...hat.com, peterz@...radead.org,
tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/urgent] rcu: Clean up code based on review feedback from Josh Triplett
Commit-ID: fc2219d49ef1606e7fd2c88af2b423b01ff3d319
Gitweb: http://git.kernel.org/tip/fc2219d49ef1606e7fd2c88af2b423b01ff3d319
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
AuthorDate: Wed, 23 Sep 2009 09:50:41 -0700
Committer: Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 23 Sep 2009 19:46:29 +0200
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@...ux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: laijs@...fujitsu.com
Cc: dipankar@...ibm.com
Cc: akpm@...ux-foundation.org
Cc: mathieu.desnoyers@...ymtl.ca
Cc: josh@...htriplett.org
Cc: dvhltc@...ibm.com
Cc: niv@...ibm.com
Cc: rostedt@...dmis.org
Cc: Valdis.Kletnieks@...edu
Cc: dhowells@...hat.com
LKML-Reference: <12537246442687-git-send-email->
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
include/linux/rcutree.h | 1 -
kernel/rcutree.c | 29 ++++++++++++++++----------
kernel/rcutree.h | 6 ++--
kernel/rcutree_plugin.h | 50 +++++++++++++++++++++++-----------------------
4 files changed, 46 insertions(+), 40 deletions(-)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 3768277..88109c8 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -85,7 +85,6 @@ static inline void synchronize_rcu_bh_expedited(void)
extern void __rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);
-extern void rcu_restart_cpu(int cpu);
extern long rcu_batches_completed(void);
extern long rcu_batches_completed_bh(void);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 52b06f6..f85b684 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -101,6 +101,16 @@ static void __cpuinit rcu_init_percpu_data(int cpu, struct rcu_state *rsp,
#include "rcutree_plugin.h"
/*
+ * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
+ * permit this function to be invoked without holding the root rcu_node
+ * structure's ->lock, but of course results can be subject to change.
+ */
+static int rcu_gp_in_progress(struct rcu_state *rsp)
+{
+ return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
+}
+
+/*
* Note a quiescent state. Because we do not need to know
* how many quiescent states passed, just if there was at least
* one since the start of the grace period, this just sets a flag.
@@ -173,9 +183,7 @@ cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
static int
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
- /* ACCESS_ONCE() because we are accessing outside of lock. */
- return *rdp->nxttail[RCU_DONE_TAIL] &&
- ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum);
+ return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
}
/*
@@ -482,7 +490,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
spin_lock_irqsave(&rnp->lock, flags);
delta = jiffies - rsp->jiffies_stall;
- if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum == rsp->completed) {
+ if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
@@ -537,8 +545,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
/* We haven't checked in, so go dump stack. */
print_cpu_stall(rsp);
- } else if (rsp->gpnum != rsp->completed &&
- delta >= RCU_STALL_RAT_DELAY) {
+ } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
/* They had two time units to dump stack, so complain. */
print_other_cpu_stall(rsp);
@@ -703,9 +710,9 @@ rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
* hold rnp->lock, as required by rcu_start_gp(), which will release it.
*/
static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags)
- __releases(rnp->lock)
+ __releases(rcu_get_root(rsp)->lock)
{
- WARN_ON_ONCE(rsp->completed == rsp->gpnum);
+ WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
rsp->completed = rsp->gpnum;
rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]);
rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
@@ -1092,7 +1099,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
struct rcu_node *rnp = rcu_get_root(rsp);
u8 signaled;
- if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum))
+ if (!rcu_gp_in_progress(rsp))
return; /* No grace period in progress, nothing to force. */
if (!spin_trylock_irqsave(&rsp->fqslock, flags)) {
rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
@@ -1251,7 +1258,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
/* Start a new grace period if one not already started. */
- if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) {
+ if (!rcu_gp_in_progress(rsp)) {
unsigned long nestflag;
struct rcu_node *rnp_root = rcu_get_root(rsp);
@@ -1331,7 +1338,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
}
/* Has an RCU GP gone long enough to send resched IPIs &c? */
- if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&
+ if (rcu_gp_in_progress(rsp) &&
((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
rdp->n_rp_need_fqs++;
return 1;
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 8e8287a..9aa8c8a 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -48,14 +48,14 @@
#elif NR_CPUS <= RCU_FANOUT_SQ
# define NUM_RCU_LVLS 2
# define NUM_RCU_LVL_0 1
-# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT)
+# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
# define NUM_RCU_LVL_2 (NR_CPUS)
# define NUM_RCU_LVL_3 0
#elif NR_CPUS <= RCU_FANOUT_CUBE
# define NUM_RCU_LVLS 3
# define NUM_RCU_LVL_0 1
-# define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ)
-# define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT))
+# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ)
+# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
# define NUM_RCU_LVL_3 NR_CPUS
#else
# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
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 @@ 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
/*
--
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