rcu: Move RCU's grace-period-change code to ->gp_seq

This commit moves __note_gp_changes(), note_gp_changes(), and
__rcu_pending() to ->gp_seq, creating new rcu_seq_completed_gp() and
rcu_seq_new_gp() functions for this purpose.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Reinstate "cpuend: trace as suggested by Joel Fernandes. ]

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index f0907f9..7568a3f 100644 (file)
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -117,6 +117,23 @@ static inline bool rcu_seq_done(unsigned long *sp, unsigned long s)
 }
 
 /*
+ * Has a grace period completed since the time the old gp_seq was collected?
+ */
+static inline bool rcu_seq_completed_gp(unsigned long old, unsigned long new)
+{
+       return ULONG_CMP_LT(old, new & ~RCU_SEQ_STATE_MASK);
+}
+
+/*
+ * Has a grace period started since the time the old gp_seq was collected?
+ */
+static inline bool rcu_seq_new_gp(unsigned long old, unsigned long new)
+{
+       return ULONG_CMP_LT((old + RCU_SEQ_STATE_MASK) & ~RCU_SEQ_STATE_MASK,
+                           new);
+}
+
+/*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
  * by call_rcu() and rcu callback execution, and are therefore not part of the
  * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index fd2f582..bcd659e 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1790,24 +1790,23 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
 
        raw_lockdep_assert_held_rcu_node(rnp);
 
-       /* Handle the ends of any preceding grace periods first. */
-       if (rdp->completed == rnp->completed &&
-           !unlikely(READ_ONCE(rdp->gpwrap))) {
-
-               /* No grace period end, so just accelerate recent callbacks. */
-               ret = rcu_accelerate_cbs(rsp, rnp, rdp);
-
-       } else {
-
-               /* Advance callbacks. */
-               ret = rcu_advance_cbs(rsp, rnp, rdp);
+       if (rdp->gp_seq == rnp->gp_seq)
+               return false; /* Nothing to do. */
 
+       /* Handle the ends of any preceding grace periods first. */
+       if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
+           unlikely(READ_ONCE(rdp->gpwrap))) {
+               ret = rcu_advance_cbs(rsp, rnp, rdp); /* Advance callbacks. */
                /* Remember that we saw this grace-period completion. */
                rdp->completed = rnp->completed;
-               trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
+               trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("cpuend"));
+       } else {
+               ret = rcu_accelerate_cbs(rsp, rnp, rdp); /* Recent callbacks. */
        }
 
-       if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
+       /* Now handle the beginnings of any new-to-this-CPU grace periods. */
+       if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
+           unlikely(READ_ONCE(rdp->gpwrap))) {
                /*
                 * If the current grace period is waiting for this CPU,
                 * set up to detect a quiescent state, otherwise don't
@@ -1823,8 +1822,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
                WRITE_ONCE(rdp->gpwrap, false);
                rcu_gpnum_ovf(rnp, rdp);
        }
-       if (rdp->gp_seq != rnp->gp_seq)
-               rdp->gp_seq = rnp->gp_seq;
+       rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */
        return ret;
 }
 
@@ -1836,8 +1834,7 @@ static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
 
        local_irq_save(flags);
        rnp = rdp->mynode;
-       if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
-            rdp->completed == READ_ONCE(rnp->completed) &&
+       if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
             !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
            !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
                local_irq_restore(flags);
@@ -3286,12 +3283,8 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
            !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
                return 1;
 
-       /* Has another RCU grace period completed?  */
-       if (READ_ONCE(rnp->completed) != rdp->completed) /* outside lock */
-               return 1;
-
-       /* Has a new RCU grace period started? */
-       if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
+       /* Have RCU grace period completed or started?  */
+       if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
            unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
                return 1;