[PATCH 1/2][PATCH][SRU][Wily][V2] rhashtable: Fix walker list corruption

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/1526811

The commit ba7c95ea3870fe7b847466d39a049ab6f156aa2c ("rhashtable:
Fix sleeping inside RCU critical section in walk_stop") introduced
a new spinlock for the walker list.  However, it did not convert
all existing users of the list over to the new spin lock.  Some
continued to use the old mutext for this purpose.  This obviously
led to corruption of the list.

The fix is to use the spin lock everywhere where we touch the list.

This also allows us to do rcu_rad_lock before we take the lock in
rhashtable_walk_start.  With the old mutex this would've deadlocked
but it's safe with the new spin lock.

Fixes: ba7c95ea3870 ("rhashtable: Fix sleeping inside RCU...")
Reported-by: Colin Ian King <colin.king at canonical.com>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: David S. Miller <davem at davemloft.net>
backported from commit c6ff5268293ef98e48a99597e765ffc417e39fa5
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 lib/rhashtable.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index cc0c697..cce0eed 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -506,10 +506,10 @@ int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
 	if (!iter->walker)
 		return -ENOMEM;
 
-	mutex_lock(&ht->mutex);
+	spin_lock(&ht->lock);
 	iter->walker->tbl = rht_dereference(ht->tbl, ht);
 	list_add(&iter->walker->list, &iter->walker->tbl->walkers);
-	mutex_unlock(&ht->mutex);
+	spin_unlock(&ht->lock);
 
 	return 0;
 }
@@ -523,10 +523,10 @@ EXPORT_SYMBOL_GPL(rhashtable_walk_init);
  */
 void rhashtable_walk_exit(struct rhashtable_iter *iter)
 {
-	mutex_lock(&iter->ht->mutex);
+	spin_lock(&iter->ht->lock);
 	if (iter->walker->tbl)
 		list_del(&iter->walker->list);
-	mutex_unlock(&iter->ht->mutex);
+	spin_unlock(&iter->ht->lock);
 	kfree(iter->walker);
 }
 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
@@ -550,14 +550,12 @@ int rhashtable_walk_start(struct rhashtable_iter *iter)
 {
 	struct rhashtable *ht = iter->ht;
 
-	mutex_lock(&ht->mutex);
+	rcu_read_lock();
 
+	spin_lock(&ht->lock);
 	if (iter->walker->tbl)
 		list_del(&iter->walker->list);
-
-	rcu_read_lock();
-
-	mutex_unlock(&ht->mutex);
+	spin_unlock(&ht->lock);
 
 	if (!iter->walker->tbl) {
 		iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht);
-- 
1.9.1