From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:60160 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751658AbdK0MXj (ORCPT ); Mon, 27 Nov 2017 07:23:39 -0500 Subject: Patch "lib/mpi: call cond_resched() from mpi_powm() loop" has been added to the 4.9-stable tree To: ebiggers@google.com, gregkh@linuxfoundation.org, herbert@gondor.apana.org.au Cc: , From: Date: Mon, 27 Nov 2017 13:23:44 +0100 Message-ID: <1511785424452@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled lib/mpi: call cond_resched() from mpi_powm() loop to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: lib-mpi-call-cond_resched-from-mpi_powm-loop.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 1d9ddde12e3c9bab7f3d3484eb9446315e3571ca Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 7 Nov 2017 14:15:27 -0800 Subject: lib/mpi: call cond_resched() from mpi_powm() loop From: Eric Biggers commit 1d9ddde12e3c9bab7f3d3484eb9446315e3571ca upstream. 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. Do the cond_resched() once per bit rather than once per MPI limb because each limb might still easily take 100+ milliseconds on slow CPUs. Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu Signed-off-by: Greg Kroah-Hartman --- lib/mpi/mpi-pow.c | 2 ++ 1 file changed, 2 insertions(+) --- a/lib/mpi/mpi-pow.c +++ b/lib/mpi/mpi-pow.c @@ -26,6 +26,7 @@ * however I decided to publish this code under the plain GPL. */ +#include #include #include "mpi-internal.h" #include "longlong.h" @@ -256,6 +257,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, } e <<= 1; c--; + cond_resched(); } i--; Patches currently in stable-queue which might be from ebiggers@google.com are queue-4.9/lib-mpi-call-cond_resched-from-mpi_powm-loop.patch