1 files changed, 18 insertions, 3 deletions

diff --git a/kernel/srcu.c b/kernel/srcu.c
index 2980da3fd509..73ce23feaea9 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -31,6 +31,7 @@
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 #include <linux/smp.h>
+#include <linux/delay.h>
 #include <linux/srcu.h>
 
 static int init_srcu_struct_fields(struct srcu_struct *sp)
@@ -46,11 +47,9 @@ static int init_srcu_struct_fields(struct srcu_struct *sp)
 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
                        struct lock_class_key *key)
 {
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
         /* Don't re-initialize a lock while it is held. */
         debug_check_no_locks_freed((void *)sp, sizeof(*sp));
         lockdep_init_map(&sp->dep_map, name, key, 0);
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
         return init_srcu_struct_fields(sp);
 }
 EXPORT_SYMBOL_GPL(__init_srcu_struct);
@@ -157,6 +156,16 @@ void __srcu_read_unlock(struct srcu_struct *sp, int idx)
 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
 
 /*
+ * We use an adaptive strategy for synchronize_srcu() and especially for
+ * synchronize_srcu_expedited().  We spin for a fixed time period
+ * (defined below) to allow SRCU readers to exit their read-side critical
+ * sections.  If there are still some readers after 10 microseconds,
+ * we repeatedly block for 1-millisecond time periods.  This approach
+ * has done well in testing, so there is no need for a config parameter.
+ */
+#define SYNCHRONIZE_SRCU_READER_DELAY 10
+
+/*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
 static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
@@ -205,9 +214,15 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
          * all srcu_read_lock() calls using the old counters have completed.
          * Their corresponding critical sections might well be still
          * executing, but the srcu_read_lock() primitives themselves
-         * will have finished executing.
+         * will have finished executing.  We initially give readers
+         * an arbitrarily chosen 10 microseconds to get out of their
+         * SRCU read-side critical sections, then loop waiting 1/HZ
+         * seconds per iteration.  The 10-microsecond value has done
+         * very well in testing.
          */
 
+        if (srcu_readers_active_idx(sp, idx))
+                udelay(SYNCHRONIZE_SRCU_READER_DELAY);
         while (srcu_readers_active_idx(sp, idx))
                 schedule_timeout_interruptible(1);