From patchwork Fri Oct 21 15:58:50 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Doug Anderson X-Patchwork-Id: 9389579 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 045D0607D0 for ; Fri, 21 Oct 2016 16:00:07 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id EAB9B2A09D for ; Fri, 21 Oct 2016 16:00:06 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DDB202A0A0; Fri, 21 Oct 2016 16:00:06 +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 59D6A2A097 for ; Fri, 21 Oct 2016 16:00:06 +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 1bxcEm-0000kZ-NH; Fri, 21 Oct 2016 16:00:04 +0000 Received: from mail-pf0-x233.google.com ([2607:f8b0:400e:c00::233]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bxcEb-0000Fv-25 for linux-rockchip@lists.infradead.org; Fri, 21 Oct 2016 16:00:01 +0000 Received: by mail-pf0-x233.google.com with SMTP id e6so58946703pfk.3 for ; Fri, 21 Oct 2016 08:59:32 -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=zbSwb4wWTm6NRyb4X+OMEqGBSMWrtkfiM7GynywY7dg=; b=WxYCWLQ5ZT+aQyNFHGeSZ8TCtEDR+dtNhfDJzbW0pYBnVOummWLlxsn81iGhOQZnrX 5JXtRO8zuQ4AEwYtNYZlij4fPG0xtbZVfb8QodC9EPuYfhEuwxbwUn914gPylrQAwawj kdNddOCGGP8dx2UK8q4qT4RiqgCYzBQBHFclA= 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=zbSwb4wWTm6NRyb4X+OMEqGBSMWrtkfiM7GynywY7dg=; b=IcTv9UMU8Wemjpn1MKJ+Orud8Q+xDEJlSy6OK8hYiChB8dCwMHlhBYqX5anlU7ddRM /C+6oSBUD0cIU1/v2LgZELiDQSvQKtylSGp6QW5wGtHa1B/JGYqbCfiHf/ckrDeiHbvQ nHai+a6aVoUvVTd9Nz4L+c5SUmPRtDejBUo57ddkjzIvZsK7TiHiiTg5d/jtVz4XiVQb Y/Ajxus5x0H6GXlF+Q+HaKYz4tSP2ZkNUvs7UHnWfZVBC9+Mz5oDk9KqamKvA5g11kk8 anMfry+dHBsPJ2M/2+tCpKAozPDGxVVXVIVSHH2GHMYafGf8x/IXjScYxLu9cTodlVmt 560w== X-Gm-Message-State: ABUngveLUdmvkhc2Cd+iCxEdRJF3FTZq8+tx+AUp/9LOM+FXBzIV6pkE/kdzWZWGRSLn+I+j X-Received: by 10.99.115.65 with SMTP id d1mr2337019pgn.56.1477065571460; Fri, 21 Oct 2016 08:59:31 -0700 (PDT) Received: from chromelab4.mtv.corp.google.com ([100.98.62.8]) by smtp.gmail.com with ESMTPSA id f1sm6234114pfa.29.2016.10.21.08.59.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 21 Oct 2016 08:59:30 -0700 (PDT) From: Douglas Anderson To: Thomas Gleixner , John Stultz Subject: [PATCH v5 1/2] timers: Fix usleep_range() in the context of wake_up_process() Date: Fri, 21 Oct 2016 08:58:50 -0700 Message-Id: <1477065531-30342-1-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-20161021_085953_496391_8502CEA8 X-CRM114-Status: GOOD ( 16.58 ) 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 98896 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 --- Changes in v5: - Don't accidentally busy wait after first wakeup (Thomas Gleixner) - Removed Reviewed-by tags Changes in v4: None 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 | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 32bf6f75a8fe..ab65e7bcc2c2 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1896,16 +1896,6 @@ unsigned long msleep_interruptible(unsigned int msecs) EXPORT_SYMBOL(msleep_interruptible); -static void __sched do_usleep_range(unsigned long min, unsigned long max) -{ - ktime_t kmin; - u64 delta; - - kmin = ktime_set(0, min * NSEC_PER_USEC); - delta = (u64)(max - min) * NSEC_PER_USEC; - schedule_hrtimeout_range(&kmin, delta, HRTIMER_MODE_REL); -} - /** * usleep_range - Sleep for an approximate time * @min: Minimum time in usecs to sleep @@ -1919,7 +1909,15 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max) */ void __sched usleep_range(unsigned long min, unsigned long max) { - __set_current_state(TASK_UNINTERRUPTIBLE); - do_usleep_range(min, max); + ktime_t expires = ktime_add_us(ktime_get(), min); + u64 delta = (u64)(max - min) * NSEC_PER_USEC; + + for (;;) { + __set_current_state(TASK_UNINTERRUPTIBLE); + /* Do not return before the requested sleep time has elapsed */ + if (!schedule_hrtimeout_range(&expires, delta, + HRTIMER_MODE_ABS)) + break; + } } EXPORT_SYMBOL(usleep_range);