From patchwork Tue Jul 17 18:05:41 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: john stultz X-Patchwork-Id: 10065 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id 905CC23E2F for ; Tue, 17 Jul 2012 18:07:21 +0000 (UTC) Received: from mail-yw0-f52.google.com (mail-yw0-f52.google.com [209.85.213.52]) by fiordland.canonical.com (Postfix) with ESMTP id 5DE87A182D0 for ; Tue, 17 Jul 2012 18:07:21 +0000 (UTC) Received: by mail-yw0-f52.google.com with SMTP id p61so756411yhp.11 for ; Tue, 17 Jul 2012 11:07:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-forwarded-to:x-forwarded-for:delivered-to:received-spf:from:to:cc :subject:date:message-id:x-mailer:in-reply-to:references :x-content-scanned:x-cbid:x-gm-message-state; bh=JF7A2zqd/rlLszZ2lJx08h6TdE72m98vmWZ3NUXD0Rk=; b=kDTIJ19q4vae/tjx2YhLPaSGhK5IExqOF70XsQVHmYcuVtX8LQsc400Or5bPB1YuPl KZIMNQl7assD0VrV5+fDSV2dZkb0fvaAf0+ro0Q0t7nuth1AbPKuQ69Av5Es9gGcUVeA 2OnqEGFQJ9bneU2iHuLiUkRI3qh4prA8ERj4f3eFSRmwHEiLX0ih8HzwtejSvdQXX2JL 3x9dxR0Vaq9b3NFGLlpg57/GVhmsUGsRA56kHEZSIIok897Bu/UlMmtDi5RcwNWdcdSE 0JvqpyhjGJrFDHE2i7qn+kwZZKVDig6TtYdezwYuZFlKEDTWyzuQQS40G2yQd03NW0Op x+aA== Received: by 10.50.160.198 with SMTP id xm6mr2293237igb.0.1342548440924; Tue, 17 Jul 2012 11:07:20 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.231.241.2 with SMTP id lc2csp22947ibb; Tue, 17 Jul 2012 11:07:20 -0700 (PDT) Received: by 10.60.25.38 with SMTP id z6mr4746254oef.15.1342548439931; Tue, 17 Jul 2012 11:07:19 -0700 (PDT) Received: from e33.co.us.ibm.com (e33.co.us.ibm.com. [32.97.110.151]) by mx.google.com with ESMTPS id q10si18988983oeh.3.2012.07.17.11.07.19 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 17 Jul 2012 11:07:19 -0700 (PDT) Received-SPF: pass (google.com: domain of johnstul@us.ibm.com designates 32.97.110.151 as permitted sender) client-ip=32.97.110.151; Authentication-Results: mx.google.com; spf=pass (google.com: domain of johnstul@us.ibm.com designates 32.97.110.151 as permitted sender) smtp.mail=johnstul@us.ibm.com Received: from /spool/local by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 17 Jul 2012 12:07:16 -0600 Received: from d03dlp03.boulder.ibm.com (9.17.202.179) by e33.co.us.ibm.com (192.168.1.133) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Tue, 17 Jul 2012 12:06:42 -0600 Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 4DDE819D804C for ; Tue, 17 Jul 2012 18:06:39 +0000 (WET) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q6HI6D0K123822 for ; Tue, 17 Jul 2012 12:06:19 -0600 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q6HI6BF5019655 for ; Tue, 17 Jul 2012 12:06:11 -0600 Received: from kernel.stglabs.ibm.com (kernel.stglabs.ibm.com [9.114.214.19]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q6HI60xo018372; Tue, 17 Jul 2012 12:06:10 -0600 From: John Stultz To: stable@vger.kernel.org Cc: John Stultz , Thomas Gleixner , Prarit Bhargava , Linux Kernel Subject: [PATCH 10/11] 2.6.35.x: hrtimer: Update hrtimer base offsets each hrtimer_interrupt Date: Tue, 17 Jul 2012 14:05:41 -0400 Message-Id: <1342548342-19683-11-git-send-email-johnstul@us.ibm.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1342548342-19683-1-git-send-email-johnstul@us.ibm.com> References: <1342548342-19683-1-git-send-email-johnstul@us.ibm.com> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12071718-2398-0000-0000-00000892FFF6 X-Gm-Message-State: ALoCoQl1WcItFhcwDLZNLx2fI541yzniDIxqR1dhoLZma0smJZ381v9xkq67aZrUWzaXYrmumxBZ This is a backport of 5baefd6d84163443215f4a99f6a20f054ef11236 The update of the hrtimer base offsets on all cpus cannot be made atomically from the timekeeper.lock held and interrupt disabled region as smp function calls are not allowed there. clock_was_set(), which enforces the update on all cpus, is called either from preemptible process context in case of do_settimeofday() or from the softirq context when the offset modification happened in the timer interrupt itself due to a leap second. In both cases there is a race window for an hrtimer interrupt between dropping timekeeper lock, enabling interrupts and clock_was_set() issuing the updates. Any interrupt which arrives in that window will see the new time but operate on stale offsets. So we need to make sure that an hrtimer interrupt always sees a consistent state of time and offsets. ktime_get_update_offsets() allows us to get the current monotonic time and update the per cpu hrtimer base offsets from hrtimer_interrupt() to capture a consistent state of monotonic time and the offsets. The function replaces the existing ktime_get() calls in hrtimer_interrupt(). The overhead of the new function vs. ktime_get() is minimal as it just adds two store operations. This ensures that any changes to realtime or boottime offsets are noticed and stored into the per-cpu hrtimer base structures, prior to any hrtimer expiration and guarantees that timers are not expired early. Signed-off-by: John Stultz Reviewed-by: Ingo Molnar Acked-by: Peter Zijlstra Acked-by: Prarit Bhargava Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1341960205-56738-8-git-send-email-johnstul@us.ibm.com Signed-off-by: Thomas Gleixner Cc: Prarit Bhargava Cc: Thomas Gleixner Cc: Linux Kernel Signed-off-by: John Stultz --- kernel/hrtimer.c | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-) diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 2f05eb1..85b5cfc 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -603,6 +603,12 @@ static int hrtimer_reprogram(struct hrtimer *timer, return res; } +static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base) +{ + ktime_t *offs_real = &base->clock_base[CLOCK_REALTIME].offset; + + return ktime_get_update_offsets(offs_real); +} /* * Retrigger next event is called after clock was set @@ -612,26 +618,15 @@ static int hrtimer_reprogram(struct hrtimer *timer, static void retrigger_next_event(void *arg) { struct hrtimer_cpu_base *base; - struct timespec realtime_offset; - unsigned long seq; if (!hrtimer_hres_active()) return; - do { - seq = read_seqbegin(&xtime_lock); - set_normalized_timespec(&realtime_offset, - -wall_to_monotonic.tv_sec, - -wall_to_monotonic.tv_nsec); - } while (read_seqretry(&xtime_lock, seq)); - base = &__get_cpu_var(hrtimer_bases); /* Adjust CLOCK_REALTIME offset */ raw_spin_lock(&base->lock); - base->clock_base[CLOCK_REALTIME].offset = - timespec_to_ktime(realtime_offset); - + hrtimer_update_base(base); hrtimer_force_reprogram(base, 0); raw_spin_unlock(&base->lock); } @@ -731,7 +726,6 @@ static int hrtimer_switch_to_hres(void) base->clock_base[CLOCK_MONOTONIC].resolution = KTIME_HIGH_RES; tick_setup_sched_timer(); - /* "Retrigger" the interrupt to get things going */ retrigger_next_event(NULL); local_irq_restore(flags); @@ -1280,7 +1274,7 @@ void hrtimer_interrupt(struct clock_event_device *dev) dev->next_event.tv64 = KTIME_MAX; raw_spin_lock(&cpu_base->lock); - entry_time = now = ktime_get(); + entry_time = now = hrtimer_update_base(cpu_base); retry: expires_next.tv64 = KTIME_MAX; /* @@ -1356,9 +1350,12 @@ retry: * We need to prevent that we loop forever in the hrtimer * interrupt routine. We give it 3 attempts to avoid * overreacting on some spurious event. + * + * Acquire base lock for updating the offsets and retrieving + * the current time. */ raw_spin_lock(&cpu_base->lock); - now = ktime_get(); + now = hrtimer_update_base(cpu_base); cpu_base->nr_retries++; if (++retries < 3) goto retry;