rhashtable: Fix rhashtable_try_insert test

BugLink: https://bugs.launchpad.net/bugs/2103829

[ Upstream commit 9d4f8e54cef2c42e23ef258833dbd06a1eaff89b ]

The test on whether rhashtable_insert_one did an insertion relies
on the value returned by rhashtable_lookup_one.  Unfortunately that
value is overwritten after rhashtable_insert_one returns.  Fix this
by moving the test before data gets overwritten.

Simplify the test as only data == NULL matters.

Finally move atomic_inc back within the lock as otherwise it may
be reordered with the atomic_dec on the removal side, potentially
leading to an underflow.

Reported-by: Michael Kelley <mhklinux@outlook.com>
Fixes: e1d3422c95f0 ("rhashtable: Fix potential deadlock by moving schedule_work outside lock")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Tested-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Noah Wager <noah.wager@canonical.com>
Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>

Author: herbertx

lib/rhashtable.c

@@ -611,21 +611,23 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
 			new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 			data = ERR_PTR(-EAGAIN);
 		} else {
+			bool inserted;
+
 			flags = rht_lock(tbl, bkt);
 			data = rhashtable_lookup_one(ht, bkt, tbl,
 						     hash, key, obj);
 			new_tbl = rhashtable_insert_one(ht, bkt, tbl,
 							hash, obj, data);
+			inserted = data && !new_tbl;
+			if (inserted)
+				atomic_inc(&ht->nelems);
 			if (PTR_ERR(new_tbl) != -EEXIST)
 				data = ERR_CAST(new_tbl);
 
 			rht_unlock(tbl, bkt, flags);
 
-			if (PTR_ERR(data) == -ENOENT && !new_tbl) {
-				atomic_inc(&ht->nelems);
-				if (rht_grow_above_75(ht, tbl))
-					schedule_work(&ht->run_work);
-			}
+			if (inserted && rht_grow_above_75(ht, tbl))
+				schedule_work(&ht->run_work);
 		}
 	} while (!IS_ERR_OR_NULL(new_tbl));