From 969f0220b3f4ad77c09ca401ec78f354c7003256 Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Sun, 15 Mar 2015 21:12:05 +1100 Subject: [PATCH] rhashtable: Fix rhashtable_remove failures The commit 76bff2ee499f60150ad7747903abecb0b21f1479 ("rhashtable: Free bucket tables asynchronously after rehash") causes gratuitous failures in rhashtable_remove. The reason is that it inadvertently introduced multiple rehashing from the perspective of readers. IOW it is now possible to see more than two tables during a single RCU critical section. Fortunately the other reader rhashtable_lookup already deals with this correctly thanks to 62cd523211c1e03eb4ce7e0618396a526602cbac ("rhashtable: rhashtable: Move future_tbl into struct bucket_table") so only rhashtable_remove is broken by this change. This patch fixes this by looping over every table from the first one to the last or until we find the element that we were trying to delete. Incidentally the simple test for detecting rehashing to prevent starting another shrinking no longer works. Since it isn't needed anyway (the work queue and the mutex serves as a natural barrier to unnecessary rehashes) I've simply killed the test. Signed-off-by: Herbert Xu Signed-off-by: David S. Miller --- lib/rhashtable.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/lib/rhashtable.c b/lib/rhashtable.c index b916679b3e3b7..c523d3a563aa8 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -511,28 +511,25 @@ static bool __rhashtable_remove(struct rhashtable *ht, */ bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj) { - struct bucket_table *tbl, *old_tbl; + struct bucket_table *tbl; bool ret; rcu_read_lock(); - old_tbl = rht_dereference_rcu(ht->tbl, ht); - ret = __rhashtable_remove(ht, old_tbl, obj); + tbl = rht_dereference_rcu(ht->tbl, ht); /* Because we have already taken (and released) the bucket * lock in old_tbl, if we find that future_tbl is not yet * visible then that guarantees the entry to still be in - * old_tbl if it exists. + * the old tbl if it exists. */ - tbl = rht_dereference_rcu(old_tbl->future_tbl, ht) ?: old_tbl; - if (!ret && old_tbl != tbl) - ret = __rhashtable_remove(ht, tbl, obj); + while (!(ret = __rhashtable_remove(ht, tbl, obj)) && + (tbl = rht_dereference_rcu(tbl->future_tbl, ht))) + ; if (ret) { - bool no_resize_running = tbl == old_tbl; - atomic_dec(&ht->nelems); - if (no_resize_running && rht_shrink_below_30(ht, tbl)) + if (rht_shrink_below_30(ht, tbl)) schedule_work(&ht->run_work); } -- 2.39.5