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Commit 80ca8c3a authored by Thomas Graf's avatar Thomas Graf Committed by David S. Miller
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rhashtable: Lower/upper bucket may map to same lock while shrinking 



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: default avatarFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarThomas Graf <tgraf@suug.ch>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent df8a39de

lib/rhashtable.c

+12 −3
Original line number Diff line number Diff line
@@ -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);



		/* 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]);
@@ -452,6 +460,7 @@ int rhashtable_shrink(struct rhashtable *ht) 
				   tbl->buckets[new_hash + new_tbl->size]);



		spin_unlock_bh(new_bucket_lock);

		if (old_bucket_lock1 != old_bucket_lock2)

			spin_unlock_bh(old_bucket_lock2);

		spin_unlock_bh(old_bucket_lock1);

	}