From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: rhashtable: Prevent spurious EBUSY errors on insertion Date: Fri, 04 Dec 2015 14:38:44 -0500 (EST) Message-ID: <20151204.143844.1840501199234860407.davem@davemloft.net> References: <20151130101401.GA17712@orbit.nwl.cc> <20151130101859.GA8378@gondor.apana.org.au> <20151203124129.GA5505@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: phil@nwl.cc, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, tgraf@suug.ch, fengguang.wu@intel.com, wfg@linux.intel.com, lkp@01.org To: herbert@gondor.apana.org.au Return-path: In-Reply-To: <20151203124129.GA5505@gondor.apana.org.au> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Herbert Xu Date: Thu, 3 Dec 2015 20:41:29 +0800 > Thomas and Phil observed that under stress rhashtable insertion > sometimes failed with EBUSY, even though this error should only > ever been seen when we're under attack and our hash chain length > has grown to an unacceptable level, even after a rehash. > > It turns out that the logic for detecting whether there is an > existing rehash is faulty. In particular, when two threads both > try to grow the same table at the same time, one of them may see > the newly grown table and thus erroneously conclude that it had > been rehashed. This is what leads to the EBUSY error. > > This patch fixes this by remembering the current last table we > used during insertion so that rhashtable_insert_rehash can detect > when another thread has also done a resize/rehash. When this is > detected we will give up our resize/rehash and simply retry the > insertion with the new table. > > Reported-by: Thomas Graf > Reported-by: Phil Sutter > Signed-off-by: Herbert Xu Looks good, applied, thanks Herbert.