From patchwork Mon Oct 10 18:47:57 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 9369855 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D03CC60487 for ; Mon, 10 Oct 2016 18:48:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C47B4299B1 for ; Mon, 10 Oct 2016 18:48:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B85F8299C2; Mon, 10 Oct 2016 18:48:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 40CCA299B1 for ; Mon, 10 Oct 2016 18:48:53 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1btfd4-0004V5-Mf; Mon, 10 Oct 2016 18:48:50 +0000 Received: from mail-pa0-x229.google.com ([2607:f8b0:400e:c03::229]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1btfcz-0004LI-Kt for linux-rockchip@lists.infradead.org; Mon, 10 Oct 2016 18:48:48 +0000 Received: by mail-pa0-x229.google.com with SMTP id qn10so55428507pac.2 for ; Mon, 10 Oct 2016 11:48:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id; bh=0EuoOUa9bbpXbbSRKTzv0FU/Cur2qgGrmD/t2wJQZOU=; b=gzGYpNJmY190drDLaMmEtGDpOROlmM1kX9w0YucCPG6dBGsHhaECkfYF+GV0nzooyt oML4GCIzpO0XDSLlHdzRGmb41hS9QZsRROO+lUjarz0HF80DKTycsyWJcUOvYSaI91d0 POh1zNtWAh52tqsUc6pKEBkzJMZuUzTUJhsqY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=0EuoOUa9bbpXbbSRKTzv0FU/Cur2qgGrmD/t2wJQZOU=; b=WLJ6Rmw1mkL2Sj+ZWUbAS89esPe33cydhWNm99B1yWCm6YjU0YlNpoU/q1kV3HBchR XyFcfG/un8V8mCFuag2kYJV9oESef5z8U7TghjvlX7yCLPunucUaAC3sbmjhb8m/fNJq dOHLBWiwgqJ3HykryOdcQ4vBnsFsHAnNrxwVHgXjeextyK6TnKCLFmYUQph4bwoDKkDU OJFrBFiuiraq1m90XynxX8mc7cng5ZX2ntD0msk4I+vizRFwr6JJ7z7ECj73aDTN5pV2 ddY3uMbWJc0z+cqFDJjmQW1jOq0Td9aEWyjEFWi6W1z9IRI0498E1qBZRJvKViEtCnBG 8/Yg== X-Gm-Message-State: AA6/9RmkDOex/0QUUSlIcdVFhsKCFGZvbtHqru94genQFeTGhqVcJHgScUZGiQ+0w7fK4k10 X-Received: by 10.66.150.202 with SMTP id uk10mr57806705pab.10.1476125304606; Mon, 10 Oct 2016 11:48:24 -0700 (PDT) Received: from chromelab4.mtv.corp.google.com ([100.98.62.8]) by smtp.gmail.com with ESMTPSA id f2sm158456pfj.68.2016.10.10.11.48.23 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 10 Oct 2016 11:48:23 -0700 (PDT) From: Douglas Anderson To: Thomas Gleixner , John Stultz Subject: [PATCH] timers: Fix usleep_range() in the context of wake_up_process() Date: Mon, 10 Oct 2016 11:47:57 -0700 Message-Id: <1476125277-6061-1-git-send-email-dianders@chromium.org> X-Mailer: git-send-email 2.8.0.rc3.226.g39d4020 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20161010_114845_928749_F86CC2B5 X-CRM114-Status: GOOD ( 16.03 ) X-BeenThere: linux-rockchip@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Upstream kernel work for Rockchip platforms List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: huangtao@rock-chips.com, briannorris@chromium.org, Douglas Anderson , linux-kernel@vger.kernel.org, linux-rockchip@lists.infradead.org, tony.xie@rock-chips.com MIME-Version: 1.0 Sender: "Linux-rockchip" Errors-To: linux-rockchip-bounces+patchwork-linux-rockchip=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Users of usleep_range() expect that it will _never_ return in less time than the minimum passed parameter. However, nothing in any of the code ensures this. Specifically: usleep_range() => do_usleep_range() => schedule_hrtimeout_range() => schedule_hrtimeout_range_clock() just ends up calling schedule() with an appropriate timeout set using the hrtimer. If someone else happens to wake up our task then we'll happily return from usleep_range() early. msleep() already has code to handle this case since it will loop as long as there was still time left. usleep_range() had no such loop. The problem is is easily demonstrated with a small bit of test code: static int usleep_test_task(void *data) { atomic_t *done = data; ktime_t start, end; start = ktime_get(); usleep_range(50000, 100000); end = ktime_get(); pr_info("Requested 50000 - 100000 us. Actually slept for %llu us\n", (unsigned long long)ktime_to_us(ktime_sub(end, start))); atomic_set(done, 1); return 0; } static void run_usleep_test(void) { struct task_struct *t; atomic_t done; atomic_set(&done, 0); t = kthread_run(usleep_test_task, &done, "usleep_test_task"); while (!atomic_read(&done)) { wake_up_process(t); udelay(1000); } kthread_stop(t); } If you run the above code without this patch you get things like: Requested 50000 - 100000 us. Actually slept for 967 us If you run the above code _with_ this patch, you get: Requested 50000 - 100000 us. Actually slept for 50001 us Presumably this problem was not detected before because: - It's not terribly common to use wake_up_process() directly. - Other ways for processes to wake up are not typically mixed with usleep_range(). - There aren't lotsof places that use usleep_range(), since many people call either msleep() or udelay(). Reported-by: Tao Huang Signed-off-by: Douglas Anderson --- kernel/time/timer.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 32bf6f75a8fe..ab03c7e403a4 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1898,12 +1898,29 @@ EXPORT_SYMBOL(msleep_interruptible); static void __sched do_usleep_range(unsigned long min, unsigned long max) { + ktime_t start, end; ktime_t kmin; u64 delta; + unsigned long elapsed = 0; + int ret; + + start = ktime_get(); + do { + kmin = ktime_set(0, min * NSEC_PER_USEC); + delta = (u64)(max - min) * NSEC_PER_USEC; + ret = schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL); + + /* + * If schedule_hrtimeout_range() returns 0 then we actually + * hit the timeout. If not then we need to re-calculate the + * new timeout ourselves. + */ + if (ret == 0) + break; - kmin = ktime_set(0, min * NSEC_PER_USEC); - delta = (u64)(max - min) * NSEC_PER_USEC; - schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL); + end = ktime_get(); + elapsed = ktime_to_us(ktime_sub(end, start)); + } while (elapsed < min); } /**