From patchwork Thu Oct 20 20:34:23 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 9387533 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 58125607D0 for ; Thu, 20 Oct 2016 20:35:14 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4857429BFA for ; Thu, 20 Oct 2016 20:35:14 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3BE4829C10; Thu, 20 Oct 2016 20:35:14 +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=unavailable 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 AC9E929BFA for ; Thu, 20 Oct 2016 20:35:13 +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 1bxK3S-0008QO-BS; Thu, 20 Oct 2016 20:35:10 +0000 Received: from mail-pf0-x230.google.com ([2607:f8b0:400e:c00::230]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bxK3P-0007Uy-GX for linux-rockchip@lists.infradead.org; Thu, 20 Oct 2016 20:35:09 +0000 Received: by mail-pf0-x230.google.com with SMTP id s8so42911280pfj.2 for ; Thu, 20 Oct 2016 13:34:46 -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=X3F2SxsYRsRe0bQf+zRyhxa7oTZigG6WD3kxgIIvx4c=; b=CCEiuO947pr/mNDQdCWp53+aYuZ88xRQh6eTtZSPGbYWXhJ89jIYVmGkP6lE1m1LpQ k2vwlVPSKO1YKoOOlw1AnL56851EkdhHoKgjsv5Gxzwp2W5IJ+fO2XrGppuJlwuIU4my BVNzHXCA+dxbWIxPD+bj9m/ezbcKwNdvunLdc= 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=X3F2SxsYRsRe0bQf+zRyhxa7oTZigG6WD3kxgIIvx4c=; b=A4gyIXBPGakn9ivy41HedHTgv4uy+ea+Krz59znpz1H70lIKfKhg8I+0xBCJ0Qdhmk KKLwkhjwVz8NCwEVQjmXda+G79GKjLuVCJKozAoJCxXcUyf9d9/OaW5lTUBRh/LNpD/j RLDvwEPNg8SIxhmW0Jb+yKe+2Q7WcTVq1qNiczqeMLHJVQqeGmmenZ0eWO4lEOUrLcGS RdQdgpuFDH0vRqrBbo2lrPZhef8LfYlFqdV66q6xHR/kjaOREkPlAB41uqDmyJFfNlPS K/CAevQeuaQBoTW5ZFl9SplKofysR0JEqkNoSDhl2sz/dnN4gRt6bs0kFZ62RHbOV/Tu xSCw== X-Gm-Message-State: AA6/9RkPync15LnRzsq83FL2AaL9FuDEF7fUr93SXKw7x7EgWF1yrMMPpe/Id6Lauri10ZWd X-Received: by 10.98.11.21 with SMTP id t21mr4491248pfi.131.1476995685844; Thu, 20 Oct 2016 13:34:45 -0700 (PDT) Received: from chromelab4.mtv.corp.google.com ([100.98.62.8]) by smtp.gmail.com with ESMTPSA id zh13sm73986359pab.4.2016.10.20.13.34.44 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 20 Oct 2016 13:34:44 -0700 (PDT) From: Douglas Anderson To: Thomas Gleixner , John Stultz Subject: [PATCH v3 1/2] timers: Fix usleep_range() in the context of wake_up_process() Date: Thu, 20 Oct 2016 13:34:23 -0700 Message-Id: <1476995664-15668-1-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-20161020_133507_625953_60139E5C X-CRM114-Status: GOOD ( 17.77 ) 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, heiko@sntech.de, broonie@kernel.org, briannorris@chromium.org, Douglas Anderson , Andreas Mohr , linux-kernel@vger.kernel.org, linux-rockchip@lists.infradead.org, tony.xie@rock-chips.com, djkurtz@chromium.org, linux@roeck-us.net, tskd08@gmail.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 lots of places that use usleep_range(), since many people call either msleep() or udelay(). NOTES: - An effort was made to look for users relying on the old behavior by looking for usleep_range() in the same file as wake_up_process(). No problems was found by this search, though it is conceivable that someone could have put the sleep and wakeup in two different files. - An effort was made to ask several upstream maintainers if they were aware of people relying on wake_up_process() to wake up usleep_range(). No maintainers were aware of that but they were aware of many people relying on usleep_range() never returning before the minimum. Reported-by: Tao Huang Signed-off-by: Douglas Anderson Reviewed-by: Andreas Mohr Reviewed-by: Brian Norris Reviewed-by: Guenter Roeck --- Changes in v3: - Add Reviewed-by tags - Add notes about validation Changes in v2: - Fixed stupid bug that snuck in before posting - Use ktime_before - Remove delta from the loop kernel/time/timer.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 32bf6f75a8fe..219439efd56a 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1898,12 +1898,28 @@ EXPORT_SYMBOL(msleep_interruptible); static void __sched do_usleep_range(unsigned long min, unsigned long max) { + ktime_t now, end; ktime_t kmin; u64 delta; + int ret; - kmin = ktime_set(0, min * NSEC_PER_USEC); + now = ktime_get(); + end = ktime_add_us(now, min); delta = (u64)(max - min) * NSEC_PER_USEC; - schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL); + do { + kmin = ktime_sub(end, now); + 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; + + now = ktime_get(); + } while (ktime_before(now, end)); } /**