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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-09-20 16:02:49 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-10-20 13:47:10 -0700
commit62da1921292ef789c23a7bf01d671d7572baf377 (patch)
treeaec958e9dbfe4d7fbdfe13e8a622721bc87a1313 /kernel/rcutree.c
parent6f0c0580b70c89094b3422ba81118c7b959c7556 (diff)
downloadop-kernel-dev-62da1921292ef789c23a7bf01d671d7572baf377.zip
op-kernel-dev-62da1921292ef789c23a7bf01d671d7572baf377.tar.gz
rcu: Accelerate callbacks for CPU initiating a grace period
Because grace-period initialization is carried out by a separate kthread, it might happen on a different CPU than the one that had the callback needing a grace period -- which is where the callback acceleration needs to happen. Fortunately, rcu_start_gp() holds the root rcu_node structure's ->lock, which prevents a new grace period from starting. This allows this function to safely determine that a grace period has not yet started, which in turn allows it to fully accelerate any callbacks that it has pending. This commit adds this acceleration. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcutree.c')
-rw-r--r--kernel/rcutree.c26
1 files changed, 24 insertions, 2 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 74df86b..93d6871 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1404,15 +1404,37 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
!cpu_needs_another_gp(rsp, rdp)) {
/*
* Either we have not yet spawned the grace-period
- * task or this CPU does not need another grace period.
+ * task, this CPU does not need another grace period,
+ * or a grace period is already in progress.
* Either way, don't start a new grace period.
*/
raw_spin_unlock_irqrestore(&rnp->lock, flags);
return;
}
+ /*
+ * Because there is no grace period in progress right now,
+ * any callbacks we have up to this point will be satisfied
+ * by the next grace period. So promote all callbacks to be
+ * handled after the end of the next grace period. If the
+ * CPU is not yet aware of the end of the previous grace period,
+ * we need to allow for the callback advancement that will
+ * occur when it does become aware. Deadlock prevents us from
+ * making it aware at this point: We cannot acquire a leaf
+ * rcu_node ->lock while holding the root rcu_node ->lock.
+ */
+ rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+ if (rdp->completed == rsp->completed)
+ rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
+
rsp->gp_flags = RCU_GP_FLAG_INIT;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */
+
+ /* Ensure that CPU is aware of completion of last grace period. */
+ rcu_process_gp_end(rsp, rdp);
+ local_irq_restore(flags);
+
+ /* Wake up rcu_gp_kthread() to start the grace period. */
wake_up(&rsp->gp_wq);
}
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