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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2009-09-23 18:50:41 +0200
committerIngo Molnar <mingo@elte.hu>2009-09-23 19:46:29 +0200
commitfc2219d49ef1606e7fd2c88af2b423b01ff3d319 (patch)
tree1c1cba7e4334898a98cf0e2c992e8cfef4b34979 /kernel/rcutree.c
parentfutex: Fix wakeup race by setting TASK_INTERRUPTIBLE before queue_me() (diff)
downloadlinux-fc2219d49ef1606e7fd2c88af2b423b01ff3d319.tar.xz
linux-fc2219d49ef1606e7fd2c88af2b423b01ff3d319.zip
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>
Diffstat (limited to 'kernel/rcutree.c')
-rw-r--r--kernel/rcutree.c29
1 files changed, 18 insertions, 11 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 52b06f6e158c..f85b6842d1e1 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;