From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756799AbdLOQ3z (ORCPT ); Fri, 15 Dec 2017 11:29:55 -0500 Received: from vern.gendns.com ([206.190.152.46]:40549 "EHLO vern.gendns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756697AbdLOQ3x (ORCPT ); Fri, 15 Dec 2017 11:29:53 -0500 Subject: Re: [PATCH] clk: fix spin_lock/unlock imbalance on bad clk_enable() reentrancy From: David Lechner To: linux-clk@vger.kernel.org Cc: Michael Turquette , Stephen Boyd , linux-kernel@vger.kernel.org, Jerome Brunet References: <1513122223-14932-1-git-send-email-david@lechnology.com> <32ca585d-c51d-1c85-42ba-85f0b1df0a60@lechnology.com> Message-ID: Date: Fri, 15 Dec 2017 10:29:56 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <32ca585d-c51d-1c85-42ba-85f0b1df0a60@lechnology.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - vern.gendns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lechnology.com X-Get-Message-Sender-Via: vern.gendns.com: authenticated_id: davidmain+lechnology.com/only user confirmed/virtual account not confirmed X-Authenticated-Sender: vern.gendns.com: davidmain@lechnology.com X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/12/2017 10:14 PM, David Lechner wrote: > On 12/12/2017 05:43 PM, David Lechner wrote: >> If clk_enable() is called in reentrant way and spin_trylock_irqsave() is >> not working as expected, it is possible to get a negative enable_refcnt >> which results in a missed call to spin_unlock_irqrestore(). >> >> It works like this: >> >> 1. clk_enable() is called. >> 2. clk_enable_unlock() calls spin_trylock_irqsave() and sets >>     enable_refcnt = 1. >> 3. Another clk_enable() is called before the first has returned >>     (reentrant), but somehow spin_trylock_irqsave() is returning true. >>     (I'm not sure how/why this is happening yet, but it is happening >> to me >>     with arch/arm/mach-davinci clocks that I am working on). > > I think I have figured out that since CONFIG_SMP=n and > CONFIG_DEBUG_SPINLOCK=n on my kernel that > > #define arch_spin_trylock(lock)({ barrier(); (void)(lock); 1; }) > > in include/linux/spinlock_up.h is causing the problem. > > So, basically, reentrancy of clk_enable() is broken for non-SMP systems, > but I'm not sure I know how to fix it. > > Here is what I came up with for a fix. If it looks reasonable, I will resend as a proper patch. diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index bb1b1f9..53fad5f 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -136,12 +136,23 @@ static void clk_prepare_unlock(void) mutex_unlock(&prepare_lock); } +#ifdef CONFIG_SMP +#define NO_SMP 0 +#else +#define NO_SMP 1 +#endif + static unsigned long clk_enable_lock(void) __acquires(enable_lock) { - unsigned long flags; + unsigned long flags = 0; - if (!spin_trylock_irqsave(&enable_lock, flags)) { + /* + * spin_trylock_irqsave() always returns true on non-SMP system (unless + * spin lock debugging is enabled) so don't call spin_trylock_irqsave() + * unless we are on an SMP system. + */ + if (NO_SMP || !spin_trylock_irqsave(&enable_lock, flags)) { if (enable_owner == current) { enable_refcnt++; __acquire(enable_lock);