On Tue, Mar 24, 2015 at 08:55:13AM +1100, Herbert Xu wrote:
> On Mon, Mar 23, 2015 at 02:27:58PM -0400, Sasha Levin wrote:
> >
> > Commit 963ecbd41a ("rhashtable: Fix use-after-free in
> > rhashtable_walk_stop") is causing
> > RCU warnings since the code now locks a mutex (which might sleep) within an
> > RCU critical
> > section within rhashtable_walk_stop().
>
> OK I will add a spin lock to bucket_table for this.
---8<---
rhashtable: Fix sleeping inside RCU critical section in walk_stop
The commit 963ecbd41a1026d99ec7537c050867428c397b89 ("rhashtable:
Fix use-after-free in rhashtable_walk_stop") fixed a real bug
but created another one because we may end up sleeping inside an
RCU critical section.
This patch fixes it properly by replacing the mutex with a spin
lock that specifically protects the walker lists.
Reported-by: Sasha Levin <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 57af1e9..14db673 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -133,6 +133,7 @@ struct rhashtable_params {
* @p: Configuration parameters
* @run_work: Deferred worker to expand/shrink asynchronously
* @mutex: Mutex to protect current/future table swapping
+ * @lock: Spin lock to protect walker list
* @being_destroyed: True if table is set up for destruction
*/
struct rhashtable {
@@ -144,6 +145,7 @@ struct rhashtable {
struct rhashtable_params p;
struct work_struct run_work;
struct mutex mutex;
+ spinlock_t lock;
};
/**
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 7686c1e..e96ad1a 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -256,8 +256,10 @@ static int rhashtable_rehash_table(struct rhashtable *ht)
/* Publish the new table pointer. */
rcu_assign_pointer(ht->tbl, new_tbl);
+ spin_lock(&ht->lock);
list_for_each_entry(walker, &old_tbl->walkers, list)
walker->tbl = NULL;
+ spin_unlock(&ht->lock);
/* Wait for readers. All new readers will see the new
* table, and thus no references to the old table will
@@ -635,12 +637,12 @@ void rhashtable_walk_stop(struct rhashtable_iter *iter)
ht = iter->ht;
- mutex_lock(&ht->mutex);
+ spin_lock(&ht->lock);
if (tbl->rehash < tbl->size)
list_add(&iter->walker->list, &tbl->walkers);
else
iter->walker->tbl = NULL;
- mutex_unlock(&ht->mutex);
+ spin_unlock(&ht->lock);
iter->p = NULL;
@@ -723,6 +725,7 @@ int rhashtable_init(struct rhashtable *ht,
memset(ht, 0, sizeof(*ht));
mutex_init(&ht->mutex);
+ spin_lock_init(&ht->lock);
memcpy(&ht->p, params, sizeof(*params));
if (params->min_size)
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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