From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754136AbaFJTtQ (ORCPT ); Tue, 10 Jun 2014 15:49:16 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35085 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753987AbaFJTtN (ORCPT ); Tue, 10 Jun 2014 15:49:13 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Stuart Hayes , Thomas Gleixner , Kamal Mostafa Subject: [PATCH 3.13 118/160] hrtimer: Prevent all reprogramming if hang detected Date: Tue, 10 Jun 2014 12:45:58 -0700 Message-Id: <1402429600-20477-119-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1402429600-20477-1-git-send-email-kamal@canonical.com> References: <1402429600-20477-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.13.11.3 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Stuart Hayes commit 6c6c0d5a1c949d2e084706f9e5fb1fccc175b265 upstream. If the last hrtimer interrupt detected a hang it sets hang_detected=1 and programs the clock event device with a delay to let the system make progress. If hang_detected == 1, we prevent reprogramming of the clock event device in hrtimer_reprogram() but not in hrtimer_force_reprogram(). This can lead to the following situation: hrtimer_interrupt() hang_detected = 1; program ce device to Xms from now (hang delay) We have two timers pending: T1 expires 50ms from now T2 expires 5s from now Now T1 gets canceled, which causes hrtimer_force_reprogram() to be invoked, which in turn programs the clock event device to T2 (5 seconds from now). Any hrtimer_start after that will not reprogram the hardware due to hang_detected still being set. So we effectivly block all timers until the T2 event fires and cleans up the hang situation. Add a check for hang_detected to hrtimer_force_reprogram() which prevents the reprogramming of the hang delay in the hardware timer. The subsequent hrtimer_interrupt will resolve all outstanding issues. [ tglx: Rewrote subject and changelog and fixed up the comment in hrtimer_force_reprogram() ] Signed-off-by: Stuart Hayes Link: http://lkml.kernel.org/r/53602DC6.2060101@gmail.com Signed-off-by: Thomas Gleixner Signed-off-by: Kamal Mostafa --- kernel/hrtimer.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 383319b..0d6df7b 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -581,6 +581,23 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) cpu_base->expires_next.tv64 = expires_next.tv64; + /* + * If a hang was detected in the last timer interrupt then we + * leave the hang delay active in the hardware. We want the + * system to make progress. That also prevents the following + * scenario: + * T1 expires 50ms from now + * T2 expires 5s from now + * + * T1 is removed, so this code is called and would reprogram + * the hardware to 5s from now. Any hrtimer_start after that + * will not reprogram the hardware due to hang_detected being + * set. So we'd effectivly block all timers until the T2 event + * fires. + */ + if (cpu_base->hang_detected) + return; + if (cpu_base->expires_next.tv64 != KTIME_MAX) tick_program_event(cpu_base->expires_next, 1); } -- 1.9.1