From patchwork Fri May 8 20:47:23 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Stultz X-Patchwork-Id: 48185 Return-Path: X-Original-To: linaro@patches.linaro.org Delivered-To: linaro@patches.linaro.org Received: from mail-wi0-f200.google.com (mail-wi0-f200.google.com [209.85.212.200]) by ip-10-151-82-157.ec2.internal (Postfix) with ESMTPS id C150E21578 for ; Fri, 8 May 2015 20:47:38 +0000 (UTC) Received: by wizk4 with SMTP id k4sf10583727wiz.2 for ; Fri, 08 May 2015 13:47:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:delivered-to:from:to:cc:subject :date:message-id:x-original-sender:x-original-authentication-results :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-unsubscribe; bh=/52lsAtxTZ0tQSRigUT8c+MqOJPXowyl8wVwSPd6eak=; b=hO8R25Co0dAtgPJyNVGpFmfuZOqiFYtbal9nJLgivUHGH+xHW3rSx7sbWMLOVB5m2v A0Ml9UTNSCZXE49jfbztHcCsXhXhcg/W1AXO7iPb+qMR40ItLaKN9Qv9c1dmAtGgSghK S4OdvFJWIf+P3b6fd5QBYc7cw+twezaEE44Sz7Sf6K/Nh6fcEsFzT9Qp8OWHChZnxJ4e iRvDCvRDFeuvZdJp+3aGd4mvREpMhgfxiqs2fdsqrWzbXWm8YarxYwaBN2Ji1m8gO/IY OhRxZgyLnf3M8h8ezK3VyJdpSHFQIp8i0ZxurrAgYivh2FOv2C8pvs3dWERlZ391mim5 8E9Q== X-Gm-Message-State: ALoCoQn4WGMjNSF0S2LoIQ9rTzo3td0W3Ak4EXa/1ZzAT/IrbLN+P+c47hsVTB3/4W/CAfzCCmdX X-Received: by 10.194.121.67 with SMTP id li3mr3016602wjb.3.1431118058058; Fri, 08 May 2015 13:47:38 -0700 (PDT) MIME-Version: 1.0 X-BeenThere: patchwork-forward@linaro.org Received: by 10.152.26.74 with SMTP id j10ls429375lag.7.gmail; Fri, 08 May 2015 13:47:37 -0700 (PDT) X-Received: by 10.112.161.40 with SMTP id xp8mr4166472lbb.71.1431118057891; Fri, 08 May 2015 13:47:37 -0700 (PDT) Received: from mail-lb0-f173.google.com (mail-lb0-f173.google.com. 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[209.85.192.170]) by mx.google.com with ESMTPS id g4si8522996pdi.60.2015.05.08.13.47.34 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 May 2015 13:47:35 -0700 (PDT) Received-SPF: pass (google.com: domain of john.stultz@linaro.org designates 209.85.192.170 as permitted sender) client-ip=209.85.192.170; Received: by pdbnk13 with SMTP id nk13so96884695pdb.0 for ; Fri, 08 May 2015 13:47:34 -0700 (PDT) X-Received: by 10.68.65.110 with SMTP id w14mr1418263pbs.61.1431118054234; Fri, 08 May 2015 13:47:34 -0700 (PDT) Received: from localhost.localdomain (c-67-170-153-23.hsd1.or.comcast.net. [67.170.153.23]) by mx.google.com with ESMTPSA id dc5sm6045462pbc.53.2015.05.08.13.47.32 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 08 May 2015 13:47:33 -0700 (PDT) From: John Stultz To: lkml Cc: John Stultz , Nicolas Pitre , Thomas Gleixner , Ingo Molnar , Josh Boyer , One Thousand Gnomes , Trevor Cordes , Subject: [PATCH v3] ktime: Fix ktime_divns to do signed division Date: Fri, 8 May 2015 13:47:23 -0700 Message-Id: <1431118043-23452-1-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 X-Removed-Original-Auth: Dkim didn't pass. X-Original-Sender: john.stultz@linaro.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of patch+caf_=patchwork-forward=linaro.org@linaro.org designates 209.85.217.173 as permitted sender) smtp.mail=patch+caf_=patchwork-forward=linaro.org@linaro.org Precedence: list Mailing-list: list patchwork-forward@linaro.org; contact patchwork-forward+owners@linaro.org List-ID: X-Google-Group-Id: 836684582541 List-Post: , List-Help: , List-Archive: List-Unsubscribe: , It was noted that the 32bit implementation of ktime_divns() was doing unsigned division and didn't properly handle negative values. And when a ktime helper was changed to utilize ktime_divns, it caused a regression on some IR blasters. See the following bugzilla for details: https://bugzilla.redhat.com/show_bug.cgi?id=1200353 This patch fixes the problem in ktime_divns by checking and preserving the sign bit, and then reapplying it if appropriate after the division, it also changes the return type to a s64 to make it more obvious this is expected. Nicolas also pointed out that negative dividers would cause infinite loops on 32bit systems, negative dividers is unlikely for users of this function, but out of caution this patch adds checks for negative dividers for both 32-bit (BUG_ON) and 64-bit(WARN_ON) versions to make sure no such use cases creep in. Cc: Nicolas Pitre Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Josh Boyer Cc: One Thousand Gnomes Cc: Trevor Cordes Cc: # 3.17+ for regression Tested-by: Trevor Cordes Reported-by: Trevor Cordes Signed-off-by: John Stultz Acked-by: Nicolas Pitre Acked-by: John Stultz --- New in v3: * Fix casting issue Nicolas pointed out * Use WARN_ON for 64bit case include/linux/ktime.h | 27 +++++++++++++++++++++++---- kernel/time/hrtimer.c | 11 ++++++++--- 2 files changed, 31 insertions(+), 7 deletions(-) diff --git a/include/linux/ktime.h b/include/linux/ktime.h index 5fc3d10..ab2de1c7 100644 --- a/include/linux/ktime.h +++ b/include/linux/ktime.h @@ -166,19 +166,38 @@ static inline bool ktime_before(const ktime_t cmp1, const ktime_t cmp2) } #if BITS_PER_LONG < 64 -extern u64 __ktime_divns(const ktime_t kt, s64 div); -static inline u64 ktime_divns(const ktime_t kt, s64 div) +extern s64 __ktime_divns(const ktime_t kt, s64 div); +static inline s64 ktime_divns(const ktime_t kt, s64 div) { + /* + * Negative divisors could cause an inf loop, + * so bug out here. + */ + BUG_ON(div < 0); if (__builtin_constant_p(div) && !(div >> 32)) { - u64 ns = kt.tv64; + s64 ns = kt.tv64; + int neg = (ns < 0); + + if (neg) + ns = -ns; do_div(ns, div); + if (neg) + ns = -ns; return ns; } else { return __ktime_divns(kt, div); } } #else /* BITS_PER_LONG < 64 */ -# define ktime_divns(kt, div) (u64)((kt).tv64 / (div)) +static inline s64 ktime_divns(const ktime_t kt, s64 div) +{ + /* + * 32-bit implementation cannot handle negative divisors, + * so catch them on 64bit as well. + */ + WARN_ON(div < 0); + return kt.tv64 / div; +} #endif static inline s64 ktime_to_us(const ktime_t kt) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 76d4bd9..c98ce4d 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -266,12 +266,15 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags) /* * Divide a ktime value by a nanosecond value */ -u64 __ktime_divns(const ktime_t kt, s64 div) +s64 __ktime_divns(const ktime_t kt, s64 div) { - u64 dclc; - int sft = 0; + s64 dclc; + int neg, sft = 0; dclc = ktime_to_ns(kt); + neg = (dclc < 0); + if (neg) + dclc = -dclc; /* Make sure the divisor is less than 2^32: */ while (div >> 32) { sft++; @@ -279,6 +282,8 @@ u64 __ktime_divns(const ktime_t kt, s64 div) } dclc >>= sft; do_div(dclc, (unsigned long) div); + if (neg) + dclc = -dclc; return dclc; }