srcu: Pull ->srcu_{un,}lock_count into a new srcu_ctr structure

This commit prepares for array-index-free srcu_read_lock*() by moving the
->srcu_{un,}lock_count fields into a new srcu_ctr structure.  This will
permit ->srcu_index to be replaced by a per-CPU pointer to this structure.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index b17814c9d1c7..c794d599db5c 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -17,14 +17,19 @@
 struct srcu_node;
 struct srcu_struct;
 
+/* One element of the srcu_data srcu_ctrs array. */
+struct srcu_ctr {
+	atomic_long_t srcu_locks;	/* Locks per CPU. */
+	atomic_long_t srcu_unlocks;	/* Unlocks per CPU. */
+};
+
 /*
  * Per-CPU structure feeding into leaf srcu_node, similar in function
  * to rcu_node.
  */
 struct srcu_data {
 	/* Read-side state. */
-	atomic_long_t srcu_lock_count[2];	/* Locks per CPU. */
-	atomic_long_t srcu_unlock_count[2];	/* Unlocks per CPU. */
+	struct srcu_ctr srcu_ctrs[2];		/* Locks and unlocks per CPU. */
 	int srcu_reader_flavor;			/* Reader flavor for srcu_struct structure? */
 						/* Values: SRCU_READ_FLAVOR_.*  */
 
@@ -221,7 +226,7 @@ static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
 
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
 	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
-	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); /* Y */
+	this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); /* Y */
 	barrier(); /* Avoid leaking the critical section. */
 	return idx;
 }
@@ -240,7 +245,7 @@ static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
 static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
 {
 	barrier();  /* Avoid leaking the critical section. */
-	this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);  /* Z */
+	this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_unlocks.counter);  /* Z */
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
 }