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authorPaul E. McKenney <paulmck@kernel.org>2022-04-15 20:55:42 +0300
committerPaul E. McKenney <paulmck@kernel.org>2022-07-22 03:41:56 +0300
commitd96c52fe4907c68adc5e61a0bef7aec0933223d5 (patch)
treec041d374d2f739400d88ae0b08c2d697abc1bb7e /kernel
parente4333cb20f047d96485a9416a93ae4b2ec3b27dd (diff)
downloadlinux-d96c52fe4907c68adc5e61a0bef7aec0933223d5.tar.xz
rcu: Add polled expedited grace-period primitives
This commit adds expedited grace-period functionality to RCU's polled grace-period API, adding start_poll_synchronize_rcu_expedited() and cond_synchronize_rcu_expedited(), which are similar to the existing start_poll_synchronize_rcu() and cond_synchronize_rcu() functions, respectively. Note that although start_poll_synchronize_rcu_expedited() can be invoked very early, the resulting expedited grace periods are not guaranteed to start until after workqueues are fully initialized. On the other hand, both synchronize_rcu() and synchronize_rcu_expedited() can also be invoked very early, and the resulting grace periods will be taken into account as they occur. [ paulmck: Apply feedback from Neeraj Upadhyay. ] Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/ Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing Cc: Brian Foster <bfoster@redhat.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Ian Kent <raven@themaw.net> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/tree.c17
-rw-r--r--kernel/rcu/tree.h7
-rw-r--r--kernel/rcu/tree_exp.h85
3 files changed, 104 insertions, 5 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1505b02b4e53..6cf5b51622cd 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4027,20 +4027,20 @@ EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
/**
* cond_synchronize_rcu - Conditionally wait for an RCU grace period
*
- * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
+ * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
*
* If a full RCU grace period has elapsed since the earlier call to
* get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
* Otherwise, invoke synchronize_rcu() to wait for a full grace period.
*
- * Yes, this function does not take counter wrap into account. But
- * counter wrap is harmless. If the counter wraps, we have waited for
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
- * so waiting for one additional grace period should be just fine.
+ * so waiting for a couple of additional grace periods should be just fine.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
- * to the function that provided @oldstate, and that returned at the end
+ * to the function that provided @oldstate and that returned at the end
* of this function.
*/
void cond_synchronize_rcu(unsigned long oldstate)
@@ -4793,6 +4793,9 @@ static void __init rcu_init_one(void)
init_waitqueue_head(&rnp->exp_wq[3]);
spin_lock_init(&rnp->exp_lock);
mutex_init(&rnp->boost_kthread_mutex);
+ raw_spin_lock_init(&rnp->exp_poll_lock);
+ rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+ INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
}
}
@@ -5018,6 +5021,10 @@ void __init rcu_init(void)
qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
else
qovld_calc = qovld;
+
+ // Kick-start any polled grace periods that started early.
+ if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))
+ (void)start_poll_synchronize_rcu_expedited();
}
#include "tree_stall.h"
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 5634e76106c4..fb77deca5f5c 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -133,6 +133,10 @@ struct rcu_node {
wait_queue_head_t exp_wq[4];
struct rcu_exp_work rew;
bool exp_need_flush; /* Need to flush workitem? */
+ raw_spinlock_t exp_poll_lock;
+ /* Lock and data for polled expedited grace periods. */
+ unsigned long exp_seq_poll_rq;
+ struct work_struct exp_poll_wq;
} ____cacheline_internodealigned_in_smp;
/*
@@ -484,3 +488,6 @@ static void rcu_iw_handler(struct irq_work *iwp);
static void check_cpu_stall(struct rcu_data *rdp);
static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
const unsigned long gpssdelay);
+
+/* Forward declarations for tree_exp.h. */
+static void sync_rcu_do_polled_gp(struct work_struct *wp);
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index e0258066b881..571b0a700cce 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -962,3 +962,88 @@ void synchronize_rcu_expedited(void)
synchronize_rcu_expedited_destroy_work(&rew);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/*
+ * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
+ * RCU grace periods that it needs.
+ */
+static void sync_rcu_do_polled_gp(struct work_struct *wp)
+{
+ unsigned long flags;
+ struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
+ unsigned long s;
+
+ raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+ s = rnp->exp_seq_poll_rq;
+ rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+ raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+ if (s == RCU_GET_STATE_COMPLETED)
+ return;
+ while (!poll_state_synchronize_rcu(s))
+ synchronize_rcu_expedited();
+ raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+ s = rnp->exp_seq_poll_rq;
+ if (poll_state_synchronize_rcu(s))
+ rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+ raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+}
+
+/**
+ * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
+ *
+ * Returns a cookie to pass to a call to cond_synchronize_rcu(),
+ * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
+ * allowing them to determine whether or not any sort of grace period has
+ * elapsed in the meantime. If the needed expedited grace period is not
+ * already slated to start, initiates that grace period.
+ */
+unsigned long start_poll_synchronize_rcu_expedited(void)
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ unsigned long s;
+
+ s = get_state_synchronize_rcu();
+ rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
+ rnp = rdp->mynode;
+ if (rcu_init_invoked())
+ raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+ if (!poll_state_synchronize_rcu(s)) {
+ rnp->exp_seq_poll_rq = s;
+ if (rcu_init_invoked())
+ queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
+ }
+ if (rcu_init_invoked())
+ raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+
+ return s;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
+
+/**
+ * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
+ *
+ * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
+ *
+ * If any type of full RCU grace period has elapsed since the earlier
+ * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
+ * or start_poll_synchronize_rcu_expedited(), just return. Otherwise,
+ * invoke synchronize_rcu_expedited() to wait for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for a couple of additional grace periods should be just fine.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @oldstate and that returned at the end
+ * of this function.
+ */
+void cond_synchronize_rcu_expedited(unsigned long oldstate)
+{
+ if (!poll_state_synchronize_rcu(oldstate))
+ synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);