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>

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 33c1c69..91494d7 100644 (file)
--- a/include/linux/srcu.h
+++ b/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
 
 /**

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 680c96d..f0e1d44 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/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. */
 }
 

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 76ac5f5..622792a 100644 (file)
--- a/kernel/rcu/srcutiny.c
+++ b/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

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index fb560fc..b4123d7 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/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