[PATCH 6/8] srcu: update the comments of synchronize_srcu()

[Lai Jiangshan <laijs@cn.fujitsu.com>]

The core of srcu is changed, but the comments of synchronize_srcu()
describe the old algorithm. Update it to match the new algorithm.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
 kernel/srcu.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/srcu.c b/kernel/srcu.c
index ac08970..55524f6 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -446,10 +446,12 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
  * synchronize_srcu - wait for prior SRCU read-side critical-section completion
  * @sp: srcu_struct with which to synchronize.
  *
- * Flip the completed counter, and wait for the old count to drain to zero.
- * As with classic RCU, the updater must use some separate means of
- * synchronizing concurrent updates.  Can block; must be called from
- * process context.
+ * Wait for the count to drain to zero of both indexes. To avoid the
+ * possible starvation of synchronize_srcu(), it waits for the count of
+ * the index=((->completed & 1) ^ 1) to drain to zero at first,
+ * and then flip the completed and wait for the count of the other index.
+ *
+ * Can block; must be called from process context.
  *
  * Note that it is illegal to call synchronize_srcu() from the corresponding
  * SRCU read-side critical section; doing so will result in deadlock.
-- 
1.7.4.4