srcu: Add cleanup_srcu_struct_quiesced()

The current cleanup_srcu_struct() flushes work, which prevents it
from being invoked from some workqueue contexts, as well as from
atomic (non-blocking) contexts.  This patch therefore introduced a
cleanup_srcu_struct_quiesced(), which can be invoked only after all
activity on the specified srcu_struct has completed.  This restriction
allows cleanup_srcu_struct_quiesced() to be invoked from workqueue
contexts as well as from atomic contexts.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nitzan Carmi <nitzanc@mellanox.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>

include/linux/srcu.h

@@ -69,11 +69,45 @@ struct srcu_struct { };
 
 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
 		void (*func)(struct rcu_head *head));
-void cleanup_srcu_struct(struct srcu_struct *sp);
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced);
 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
 
+/**
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+static inline void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	_cleanup_srcu_struct(sp, false);
+}
+
+/**
+ * cleanup_srcu_struct_quiesced - deconstruct a quiesced sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.  Also,
+ * all grace-period processing must have completed.
+ *
+ * "Completed" means that the last synchronize_srcu() and
+ * synchronize_srcu_expedited() calls must have returned before the call
+ * to cleanup_srcu_struct_quiesced().  It also means that the callback
+ * from the last call_srcu() must have been invoked before the call to
+ * cleanup_srcu_struct_quiesced(), but you can use srcu_barrier() to help
+ * with this last.  Violating these rules will get you a WARN_ON() splat
+ * (with high probability, anyway), and will also cause the srcu_struct
+ * to be leaked.
+ */
+static inline void cleanup_srcu_struct_quiesced(struct srcu_struct *sp)
+{
+	_cleanup_srcu_struct(sp, true);
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 /**

kernel/rcu/rcutorture.c

@@ -593,7 +593,12 @@ static void srcu_torture_init(void)
 
 static void srcu_torture_cleanup(void)
 {
-	cleanup_srcu_struct(&srcu_ctld);
+	static DEFINE_TORTURE_RANDOM(rand);
+
+	if (torture_random(&rand) & 0x800)
+		cleanup_srcu_struct(&srcu_ctld);
+	else
+		cleanup_srcu_struct_quiesced(&srcu_ctld);
 	srcu_ctlp = &srcu_ctl; /* In case of a later rcutorture run. */
 }
 

kernel/rcu/srcutiny.c

@@ -86,16 +86,19 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
  * Must invoke this after you are finished using a given srcu_struct that
  * was initialized via init_srcu_struct(), else you leak memory.
  */
-void cleanup_srcu_struct(struct srcu_struct *sp)
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
 {
 	WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
-	flush_work(&sp->srcu_work);
+	if (quiesced)
+		WARN_ON(work_pending(&sp->srcu_work));
+	else
+		flush_work(&sp->srcu_work);
 	WARN_ON(sp->srcu_gp_running);
 	WARN_ON(sp->srcu_gp_waiting);
 	WARN_ON(sp->srcu_cb_head);
 	WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
 }
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
 
 /*
  * Removes the count for the old reader from the appropriate element of

kernel/rcu/srcutree.c

@@ -366,24 +366,28 @@ static unsigned long srcu_get_delay(struct srcu_struct *sp)
 	return SRCU_INTERVAL;
 }
 
-/**
- * cleanup_srcu_struct - deconstruct a sleep-RCU structure
- * @sp: structure to clean up.
- *
- * Must invoke this after you are finished using a given srcu_struct that
- * was initialized via init_srcu_struct(), else you leak memory.
- */
-void cleanup_srcu_struct(struct srcu_struct *sp)
+/* Helper for cleanup_srcu_struct() and cleanup_srcu_struct_quiesced(). */
+void _cleanup_srcu_struct(struct srcu_struct *sp, bool quiesced)
 {
 	int cpu;
 
 	if (WARN_ON(!srcu_get_delay(sp)))
-		return; /* Leakage unless caller handles error. */
+		return; /* Just leak it! */
 	if (WARN_ON(srcu_readers_active(sp)))
-		return; /* Leakage unless caller handles error. */
-	flush_delayed_work(&sp->work);
+		return; /* Just leak it! */
+	if (quiesced) {
+		if (WARN_ON(delayed_work_pending(&sp->work)))
+			return; /* Just leak it! */
+	} else {
+		flush_delayed_work(&sp->work);
+	}
 	for_each_possible_cpu(cpu)
-		flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work);
+		if (quiesced) {
+			if (WARN_ON(delayed_work_pending(&per_cpu_ptr(sp->sda, cpu)->work)))
+				return; /* Just leak it! */
+		} else {
+			flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work);
+		}
 	if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
 	    WARN_ON(srcu_readers_active(sp))) {
 		pr_info("%s: Active srcu_struct %p state: %d\n", __func__, sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)));
@@ -392,7 +396,7 @@ void cleanup_srcu_struct(struct srcu_struct *sp)
 	free_percpu(sp->sda);
 	sp->sda = NULL;
 }
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+EXPORT_SYMBOL_GPL(_cleanup_srcu_struct);
 
 /*
  * Counts the new reader in the appropriate per-CPU element of the