From patchwork Tue Feb 19 18:49:36 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Herton Ronaldo Krzesinski X-Patchwork-Id: 221843 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from chlorine.canonical.com (chlorine.canonical.com [91.189.94.204]) by ozlabs.org (Postfix) with ESMTP id 663A02C042D for ; Wed, 20 Feb 2013 05:54:55 +1100 (EST) Received: from localhost ([127.0.0.1] helo=chlorine.canonical.com) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1U7sL0-00067x-Ax; Tue, 19 Feb 2013 18:54:46 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1U7sKx-00066R-PV for kernel-team@lists.ubuntu.com; Tue, 19 Feb 2013 18:54:44 +0000 Received: from [177.16.121.6] (helo=canonical.com) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1U7sKw-0002Bl-5g; Tue, 19 Feb 2013 18:54:43 +0000 From: Herton Ronaldo Krzesinski To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Subject: [PATCH 73/81] s390/timer: avoid overflow when programming clock comparator Date: Tue, 19 Feb 2013 15:49:36 -0300 Message-Id: <1361299784-8830-74-git-send-email-herton.krzesinski@canonical.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1361299784-8830-1-git-send-email-herton.krzesinski@canonical.com> References: <1361299784-8830-1-git-send-email-herton.krzesinski@canonical.com> X-Extended-Stable: 3.5 Cc: Heiko Carstens X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.13 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: kernel-team-bounces@lists.ubuntu.com Errors-To: kernel-team-bounces@lists.ubuntu.com 3.5.7.6 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Heiko Carstens commit d911e03d097bdc01363df5d81c43f69432eb785c upstream. Since ed4f209 "s390/time: fix sched_clock() overflow" a new helper function is used to avoid overflows when converting TOD format values to nanosecond values. The kvm interrupt code formerly however only worked by accident because of an overflow. It tried to program a timer that would expire in more than ~29 years. Because of the old TOD-to-nanoseconds overflow bug the real expiry value however was much smaller, but now it isn't anymore. This however triggers yet another bug in the function that programs the clock comparator s390_next_ktime(): if the absolute "expires" value is after 2042 this will result in an overflow and the programmed value is lower than the current TOD value which immediatly triggers a clock comparator (= timer) interrupt. Since the timer isn't expired it will be programmed immediately again and so on... the result is a dead system. To fix this simply program the maximum possible value if an overflow is detected. Reported-by: Christian Borntraeger Tested-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Herton Ronaldo Krzesinski --- arch/s390/kernel/time.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c index c5531db..747ab28 100644 --- a/arch/s390/kernel/time.c +++ b/arch/s390/kernel/time.c @@ -121,6 +121,9 @@ static int s390_next_ktime(ktime_t expires, nsecs = ktime_to_ns(ktime_add(timespec_to_ktime(ts), expires)); do_div(nsecs, 125); S390_lowcore.clock_comparator = sched_clock_base_cc + (nsecs << 9); + /* Program the maximum value if we have an overflow (== year 2042) */ + if (unlikely(S390_lowcore.clock_comparator < sched_clock_base_cc)) + S390_lowcore.clock_comparator = -1ULL; set_clock_comparator(S390_lowcore.clock_comparator); return 0; }