Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756593AbdLVSmr (ORCPT ); Fri, 22 Dec 2017 13:42:47 -0500 Received: from vern.gendns.com ([206.190.152.46]:52029 "EHLO vern.gendns.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755458AbdLVSmn (ORCPT ); Fri, 22 Dec 2017 13:42:43 -0500 Subject: Re: [PATCH] clk: fix spin_lock/unlock imbalance on bad clk_enable() reentrancy To: Stephen Boyd Cc: Michael Turquette , linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, Jerome Brunet References: <1513122223-14932-1-git-send-email-david@lechnology.com> <32ca585d-c51d-1c85-42ba-85f0b1df0a60@lechnology.com> <151372258747.45969.10121622799666696251@resonance> <3ad110cf-95ba-0d0b-53ee-f1fa2d37d7fa@lechnology.com> <151379785862.37313.908268542576551305@resonance> <749e4759-3511-92d4-a19a-0f72c31b1ee6@lechnology.com> <20171220230009.GI7997@codeaurora.org> <20171222013915.GC7997@codeaurora.org> From: David Lechner Message-ID: <88c526ed-5f85-1a91-2a1d-59f9ac06559c@lechnology.com> Date: Fri, 22 Dec 2017 12:42:50 -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: <20171222013915.GC7997@codeaurora.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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 Content-Length: 3131 Lines: 111 On 12/21/2017 07:39 PM, Stephen Boyd wrote: > On 12/20, Stephen Boyd wrote: >> On 12/20, David Lechner wrote: >>> On 12/20/2017 02:33 PM, David Lechner wrote: >>> >>> >>> So, the question I have is: what is the actual "correct" behavior of >>> spin_trylock_irqsave()? Is it really supposed to always return true >>> when CONFIG_DEBUG_SPINLOCK=n and CONFIG_SMP=n or is this a bug? >> >> Thanks for doing the analysis in this thread. >> >> When CONFIG_DEBUG_SPINLOCK=n and CONFIG_SMP=n, spinlocks are >> compiler barriers, that's it. So even if it is a bug to always >> return true, I fail to see how we can detect that a spinlock is >> already held in this configuration and return true or false. >> >> I suppose the best option is to make clk_enable_lock() and >> clk_enable_unlock() into nops or pure owner/refcount/barrier >> updates when CONFIG_SMP=n. We pretty much just need the barrier >> semantics when there's only a single CPU. >> > > How about this patch? It should make the trylock go away on UP > configs and then we keep everything else for refcount and > ownership. We would test enable_owner outside of any > irqs/preemption disabled section though. That needs a think. > > ---8<---- > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c > index 3526bc068f30..b6f61367aa8d 100644 > --- a/drivers/clk/clk.c > +++ b/drivers/clk/clk.c > @@ -143,7 +143,8 @@ static unsigned long clk_enable_lock(void) > { > unsigned long flags; > > - if (!spin_trylock_irqsave(&enable_lock, flags)) { > + if (!IS_ENABLED(CONFIG_SMP) || > + !spin_trylock_irqsave(&enable_lock, flags)) { > if (enable_owner == current) { > enable_refcnt++; > __acquire(enable_lock); > > After sleeping on it, this is what I came up with. This keeps enable_owner and enable_refcnt protected and basically does the same thing that spin_lock_irqsave()/spin_unlock_irqrestore() would do on a UP system anyway, just more explicitly. --- diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index bb1b1f9..adbace3 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -136,6 +136,8 @@ static void clk_prepare_unlock(void) mutex_unlock(&prepare_lock); } +#ifdef CONFIG_SMP + static unsigned long clk_enable_lock(void) __acquires(enable_lock) { @@ -170,6 +172,43 @@ static void clk_enable_unlock(unsigned long flags) spin_unlock_irqrestore(&enable_lock, flags); } +#else + +static unsigned long clk_enable_lock(void) + __acquires(enable_lock) +{ + unsigned long flags; + + __acquire(enable_lock); + local_irq_save(flags); + preempt_disable(); + + if (enable_refcnt++ == 0) { + WARN_ON_ONCE(enable_owner != NULL); + enable_owner = current; + } else { + WARN_ON_ONCE(enable_owner != current); + } + + return flags; +} + +static void clk_enable_unlock(unsigned long flags) + __releases(enable_lock) +{ + WARN_ON_ONCE(enable_owner != current); + WARN_ON_ONCE(enable_refcnt == 0); + + if (--enable_refcnt == 0) + enable_owner = NULL; + + __release(enable_lock); + local_irq_restore(flags); + preempt_enable(); +} + +#endif + static bool clk_core_is_prepared(struct clk_core *core) { bool ret = false;