From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753128AbdKJLi6 (ORCPT ); Fri, 10 Nov 2017 06:38:58 -0500 Received: from [128.1.224.119] ([128.1.224.119]:35808 "EHLO ringil.hmeau.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753076AbdKJLi5 (ORCPT ); Fri, 10 Nov 2017 06:38:57 -0500 Date: Fri, 10 Nov 2017 22:37:30 +1100 From: Herbert Xu To: Eric Biggers Cc: linux-crypto@vger.kernel.org, Tudor-Dan Ambarus , Mat Martineau , Salvatore Benedetto , keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Biggers , stable@vger.kernel.org Subject: Re: [PATCH] lib/mpi: call cond_resched() from mpi_powm() loop Message-ID: <20171110113729.GD26163@gondor.apana.org.au> References: <20171107061951.861-1-ebiggers3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171107061951.861-1-ebiggers3@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 06, 2017 at 10:19:51PM -0800, Eric Biggers wrote: > From: Eric Biggers > > On a non-preemptible kernel, if KEYCTL_DH_COMPUTE is called with the > largest permitted inputs (16384 bits), the kernel spends 10+ seconds > doing modular exponentiation in mpi_powm() without rescheduling. If all > threads do it, it locks up the system. Moreover, it can cause > rcu_sched-stall warnings. > > Notwithstanding the insanity of doing this calculation in kernel mode > rather than in userspace, fix it by calling cond_resched() as each bit > from the exponent is processed. It's still noninterruptible, but at > least it's preemptible now. > > Cc: stable@vger.kernel.org # v4.12+ > Signed-off-by: Eric Biggers Patch applied. Thanks. -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt