rhashtable: Fix walker behaviour during rehash

Previously whenever the walker encountered a resize it simply
snaps back to the beginning and starts again.  However, this only
works if the rehash started and completed while the walker was
idle.

If the walker attempts to restart while the rehash is still ongoing,
we may miss objects that we shouldn't have.

This patch fixes this by making the walker walk the old table
followed by the new table just like all other readers.  If a
rehash is detected we will still signal our caller of the fact
so they can prepare for duplicates but we will simply continue
the walk onto the new table after the old one is finished either
by us or by the rehasher.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index c93ff8ac474a..4192682c1d5c 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -53,6 +53,7 @@ struct rhash_head {
  * @shift: Current size (1 << shift)
  * @locks_mask: Mask to apply before accessing locks[]
  * @locks: Array of spinlocks protecting individual buckets
+ * @walkers: List of active walkers
  * @buckets: size * hash buckets
  */
 struct bucket_table {
@@ -61,6 +62,7 @@ struct bucket_table {
         u32                     shift;
         unsigned int            locks_mask;
         spinlock_t              *locks;
+        struct list_head        walkers;
 
         struct rhash_head __rcu *buckets[] ____cacheline_aligned_in_smp;
 };
@@ -104,7 +106,6 @@ struct rhashtable_params {
  * @p: Configuration parameters
  * @run_work: Deferred worker to expand/shrink asynchronously
  * @mutex: Mutex to protect current/future table swapping
- * @walkers: List of active walkers
  * @being_destroyed: True if table is set up for destruction
  */
 struct rhashtable {
@@ -115,17 +116,16 @@ struct rhashtable {
         struct rhashtable_params        p;
         struct work_struct              run_work;
         struct mutex                    mutex;
-        struct list_head                walkers;
 };
 
 /**
  * struct rhashtable_walker - Hash table walker
  * @list: List entry on list of walkers
- * @resize: Resize event occured
+ * @tbl: The table that we were walking over
  */
 struct rhashtable_walker {
         struct list_head list;
-        bool resize;
+        struct bucket_table *tbl;
 };
 
 /**