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Message-Id: <20240620161142.2057652-3-paulmck@kernel.org>
Date: Thu, 20 Jun 2024 09:11:42 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
kernel-team@...a.com,
rostedt@...dmis.org,
"Paul E. McKenney" <paulmck@...nel.org>,
Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH rcu 3/3] srcu: Fill out polled grace-period APIs
This commit adds the get_completed_synchronize_srcu() and the
same_state_synchronize_srcu() functions. The first returns a cookie
that is always interpreted as corresponding to an expired grace period.
The second does an equality comparison of a pair of cookies.
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
---
include/linux/srcu.h | 31 +++++++++++++++++++++++++++++++
kernel/rcu/srcutiny.c | 3 ++-
kernel/rcu/srcutree.c | 3 ++-
3 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index f664cba7a80c2..6f6cb5fc12424 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -57,6 +57,20 @@ void cleanup_srcu_struct(struct srcu_struct *ssp);
int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
void synchronize_srcu(struct srcu_struct *ssp);
+
+#define SRCU_GET_STATE_COMPLETED 0x1
+
+/**
+ * get_completed_synchronize_srcu - Return a pre-completed polled state cookie
+ *
+ * Returns a value that poll_state_synchronize_srcu() will always treat
+ * as a cookie whose grace period has already completed.
+ */
+static inline unsigned long get_completed_synchronize_srcu(void)
+{
+ return SRCU_GET_STATE_COMPLETED;
+}
+
unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
@@ -65,6 +79,23 @@ bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
// not-yet-completed SRCU grace periods.
#define NUM_ACTIVE_SRCU_POLL_OLDSTATE 2
+/**
+ * same_state_synchronize_srcu - Are two old-state values identical?
+ * @oldstate1: First old-state value.
+ * @oldstate2: Second old-state value.
+ *
+ * The two old-state values must have been obtained from either
+ * get_state_synchronize_srcu(), start_poll_synchronize_srcu(), or
+ * get_completed_synchronize_srcu(). Returns @true if the two values are
+ * identical and @false otherwise. This allows structures whose lifetimes
+ * are tracked by old-state values to push these values to a list header,
+ * allowing those structures to be slightly smaller.
+ */
+static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned long oldstate2)
+{
+ return oldstate1 == oldstate2;
+}
+
#ifdef CONFIG_NEED_SRCU_NMI_SAFE
int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 5afd5cf494dba..549c03336ee97 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -277,7 +277,8 @@ bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
unsigned long cur_s = READ_ONCE(ssp->srcu_idx);
barrier();
- return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);
+ return cookie == SRCU_GET_STATE_COMPLETED ||
+ ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);
}
EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 15dc22a8ff5ab..d6a4047719cb0 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1543,7 +1543,8 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
*/
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
{
- if (!rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie))
+ if (cookie != SRCU_GET_STATE_COMPLETED &&
+ !rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie))
return false;
// Ensure that the end of the SRCU grace period happens before
// any subsequent code that the caller might execute.
--
2.40.1
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