srcu: expose srcu_readers_active()

This is needed by rust/helpers/srcu.c which now adds
rust_helper_srcu_readers_active() as a wrapper around the SRCU helper
for Rust callers.

To achive this:

1- Move the srcu_readers_active() implementation from
   "kernel/rcu/srcutree.c" to "include/linux/srcutree.h".

2- Implement a matching srcu_readers_active() in
   "include/linux/srcutiny.h" and use it on the existing open-coded
   WARN_ON() check in cleanup_srcu_struct().

Signed-off-by: Onur Özkan <work@onurozkan.dev>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Boqun Feng <boqun@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

2 files changed, 1 insertions, 26 deletions

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 47d48ed31848..558ba8d316db 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -85,7 +85,7 @@ EXPORT_SYMBOL_GPL(init_srcu_struct_generic);
  */
 void cleanup_srcu_struct(struct srcu_struct *ssp)
 {
-	WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
+	WARN_ON(srcu_readers_active(ssp));
 	irq_work_sync(&ssp->srcu_irq_work);
 	flush_work(&ssp->srcu_work);
 	WARN_ON(ssp->srcu_gp_running);
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 56c5db5c29a0..4a00e90e17fc 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -599,31 +599,6 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx)
 	return srcu_readers_lock_idx(ssp, idx, did_gp, unlocks);
 }
 
-/**
- * srcu_readers_active - returns true if there are readers. and false
- *                       otherwise
- * @ssp: which srcu_struct to count active readers (holding srcu_read_lock).
- *
- * Note that this is not an atomic primitive, and can therefore suffer
- * severe errors when invoked on an active srcu_struct.  That said, it
- * can be useful as an error check at cleanup time.
- */
-static bool srcu_readers_active(struct srcu_struct *ssp)
-{
-	int cpu;
-	unsigned long sum = 0;
-
-	for_each_possible_cpu(cpu) {
-		struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu);
-
-		sum += atomic_long_read(&sdp->srcu_ctrs[0].srcu_locks);
-		sum += atomic_long_read(&sdp->srcu_ctrs[1].srcu_locks);
-		sum -= atomic_long_read(&sdp->srcu_ctrs[0].srcu_unlocks);
-		sum -= atomic_long_read(&sdp->srcu_ctrs[1].srcu_unlocks);
-	}
-	return sum;
-}
-
 /*
  * We use an adaptive strategy for synchronize_srcu() and especially for
  * synchronize_srcu_expedited().  We spin for a fixed time period