[v3 PATCH] rhashtable: Still do rehash when we get EEXIST

From: Herbert Xu <herbert@gondor.apana.org.au>
To: Josh Hunt <joshhunt00@gmail.com>
Cc: Josh Elsasser <jelsasser@appneta.com>,
	"David S . Miller" <davem@davemloft.net>,
	Thomas Graf <tgraf@suug.ch>, netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: [v3 PATCH] rhashtable: Still do rehash when we get EEXIST
Date: Thu, 21 Mar 2019 09:39:52 +0800	[thread overview]
Message-ID: <20190321013952.3quw6bsqptyngzo5@gondor.apana.org.au> (raw)
In-Reply-To: <CAKA=qzY4Pzee9BVzRCciW32toeHSz7t0q9LuvQXKLG2fX9fBbg@mail.gmail.com>

On Wed, Mar 20, 2019 at 03:29:17PM -0700, Josh Hunt wrote:
>
> Herbert
> 
> We're seeing this pretty regularly on 4.14 LTS kernels. I didn't see your
> change in any of the regular trees. Are there plans to submit this? If so,
> can it get queued up for 4.14 stable too?

Hi Josh:

Thanks for reminding me.  Looks like this one slipped through the
cracks.

Dave, could you please apply this? Thanks!

---8<---
As it stands if a shrink is delayed because of an outstanding
rehash, we will go into a rescheduling loop without ever doing
the rehash.

This patch fixes this by still carrying out the rehash and then
rescheduling so that we can shrink after the completion of the
rehash should it still be necessary.

The return value of EEXIST captures this case and other cases
(e.g., another thread expanded/rehashed the table at the same
time) where we should still proceed with the rehash.

Fixes: da20420f83ea ("rhashtable: Add nested tables")
Reported-by: Josh Elsasser <jelsasser@appneta.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 852ffa5160f1..4edcf3310513 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -416,8 +416,12 @@ static void rht_deferred_worker(struct work_struct *work)
 	else if (tbl->nest)
 		err = rhashtable_rehash_alloc(ht, tbl, tbl->size);
 
-	if (!err)
-		err = rhashtable_rehash_table(ht);
+	if (!err || err == -EEXIST) {
+		int nerr;
+
+		nerr = rhashtable_rehash_table(ht);
+		err = err ?: nerr;
+	}
 
 	mutex_unlock(&ht->mutex);

-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
