Each per bucket lock covers a configurable number of buckets. While
shrinking, two buckets in the old table contain entries for a single
bucket in the new table. We need to lock down both while linking.
Check if they are protected by different locks to avoid a recursive
lock.
Fixes: 97defe1e ("rhashtable: Per bucket locks & deferred expansion/shrinking")
Reported-by: Fengguang Wu <[email protected]>
Signed-off-by: Thomas Graf <[email protected]>
---
lib/rhashtable.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 8023b55..45477f7 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -443,8 +443,16 @@ int rhashtable_shrink(struct rhashtable *ht)
new_bucket_lock = bucket_lock(new_tbl, new_hash);
spin_lock_bh(old_bucket_lock1);
- spin_lock_bh_nested(old_bucket_lock2, RHT_LOCK_NESTED);
- spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED2);
+
+ /* Depending on the lock per buckets mapping, the bucket in
+ * the lower and upper region may map to the same lock.
+ */
+ if (old_bucket_lock1 != old_bucket_lock2) {
+ spin_lock_bh_nested(old_bucket_lock2, RHT_LOCK_NESTED);
+ spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED2);
+ } else {
+ spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
+ }
rcu_assign_pointer(*bucket_tail(new_tbl, new_hash),
tbl->buckets[new_hash]);
@@ -452,7 +460,8 @@ int rhashtable_shrink(struct rhashtable *ht)
tbl->buckets[new_hash + new_tbl->size]);
spin_unlock_bh(new_bucket_lock);
- spin_unlock_bh(old_bucket_lock2);
+ if (old_bucket_lock1 != old_bucket_lock2)
+ spin_unlock_bh(old_bucket_lock2);
spin_unlock_bh(old_bucket_lock1);
}
--
1.9.3
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