From 79f92663e36969c0b6b1f8520b1171285ae3e1d3 Mon Sep 17 00:00:00 2001
From: behlendo <behlendo@7e1ea52c-4ff2-0310-8f11-9dd32ca42a1c>
Date: Mon, 7 Apr 2008 23:54:34 +0000
Subject: [PATCH] Fix race in rwlock implementation which can occur when your
 task is rescheduled to a different cpu after you've taken the lock but before
 calling RW_LOCK_HELD is called. We need the spinlock to ensure there is a
 wmb() there.

git-svn-id: https://outreach.scidac.gov/svn/spl/trunk@68 7e1ea52c-4ff2-0310-8f11-9dd32ca42a1c
---
 include/sys/rwlock.h     | 4 ++++
 modules/spl/spl-rwlock.c | 9 +++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/sys/rwlock.h b/include/sys/rwlock.h
index 6407e632d..83106846c 100644
--- a/include/sys/rwlock.h
+++ b/include/sys/rwlock.h
@@ -163,6 +163,8 @@ rw_tryenter(krwlock_t *rwlp, krw_t rw)
 				rwlp->rw_owner = current;
 			}
 			break;
+		default:
+			BUG_ON(1);
 	}
 
 	return result;
@@ -193,6 +195,8 @@ rw_enter(krwlock_t *rwlp, krw_t rw)
 			BUG_ON(rwlp->rw_owner != NULL);
 			rwlp->rw_owner = current;
 			break;
+		default:
+			BUG_ON(1);
 	}
 }
 
diff --git a/modules/spl/spl-rwlock.c b/modules/spl/spl-rwlock.c
index fa78d4c14..2ca8306f7 100644
--- a/modules/spl/spl-rwlock.c
+++ b/modules/spl/spl-rwlock.c
@@ -29,16 +29,21 @@ EXPORT_SYMBOL(__rw_write_held);
 int
 __rw_lock_held(krwlock_t *rwlp)
 {
+	int rc = 0;
+
 	BUG_ON(rwlp->rw_magic != RW_MAGIC);
 
+	spin_lock_irq(&(rwlp->rw_sem.wait_lock));
 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
 	if (rwlp->rw_sem.activity != 0) {
 #else
 	if (rwlp->rw_sem.count != 0) {
 #endif
-		return 1;
+		rc = 1;
 	}
 
-	return 0;
+	spin_unlock_irq(&(rwlp->rw_sem.wait_lock));
+
+	return rc;
 }
 EXPORT_SYMBOL(__rw_lock_held);