Patch "rhashtable: Fix walker list corruption" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

rhashtable: Fix walker list corruption

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
rhashtable-fix-walker-list-corruption.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Herbert Xu <[email protected]>
Date: Wed, 16 Dec 2015 16:45:54 +0800
Subject: rhashtable: Fix walker list corruption

From: Herbert Xu <[email protected]>

[ Upstream commit c6ff5268293ef98e48a99597e765ffc417e39fa5 ]

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.

---
 lib/rhashtable.c |   19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

@@ -506,10 +506,11 @@ int rhashtable_walk_init(struct rhashtab
 	if (!iter->walker)
 		return -ENOMEM;
 
-	mutex_lock(&ht->mutex);
-	iter->walker->tbl = rht_dereference(ht->tbl, ht);
+	spin_lock(&ht->lock);
+	iter->walker->tbl =
+		rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
 	list_add(&iter->walker->list, &iter->walker->tbl->walkers);
-	mutex_unlock(&ht->mutex);
+	spin_unlock(&ht->lock);
 
 	return 0;
 }

@@ -523,10 +524,10 @@ 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 +551,12 @@ int rhashtable_walk_start(struct rhashta
 {
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/rhashtable-fix-walker-list-corruption.patch queue-4.1/rhashtable-enforce-minimum-size-on-initial-hash-table.patch