From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C1EABC433F5 for ; Wed, 8 Dec 2021 09:10:27 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 54D016E917; Wed, 8 Dec 2021 09:10:21 +0000 (UTC) Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by gabe.freedesktop.org (Postfix) with ESMTPS id BD8DA6E8D4; Wed, 8 Dec 2021 09:10:19 +0000 (UTC) X-IronPort-AV: E=McAfee;i="6200,9189,10191"; a="261867660" X-IronPort-AV: E=Sophos;i="5.87,297,1631602800"; d="scan'208";a="261867660" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2021 01:10:19 -0800 X-IronPort-AV: E=Sophos;i="5.87,297,1631602800"; d="scan'208";a="515682918" Received: from amgotede-mobl1.ger.corp.intel.com (HELO [10.213.194.97]) ([10.213.194.97]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2021 01:10:17 -0800 Message-ID: Date: Wed, 8 Dec 2021 09:10:15 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.1 Content-Language: en-US To: Sebastian Andrzej Siewior , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org References: <20211118165914.pckik75emivsilek@linutronix.de> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: <20211118165914.pckik75emivsilek@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Intel-gfx] [PATCH] drm/i915: Don't disable interrupts and pretend a lock as been acquired in __timeline_mark_lock(). X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: David Airlie , Peter Zijlstra , Thomas Gleixner Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 18/11/2021 16:59, Sebastian Andrzej Siewior wrote: > This is a revert of commits > d67739268cf0e ("drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe") > 6c69a45445af9 ("drm/i915/gt: Mark context->active_count as protected by timeline->mutex") 6dcb85a0ad99 ("drm/i915: Hold irq-off for the entire fake lock period") is very relevant as well. > The existing code leads to a different behaviour depending on whether > lockdep is enabled or not. Any following lock that is acquired without > disabling interrupts (but needs to) will not be noticed by lockdep. Agreed this is not good. > This it not just a lockdep annotation but is used but an actual mutex_t > that is properly used as a lock but in case of __timeline_mark_lock() > lockdep is only told that it is acquired but no lock has been acquired. > > It appears that its purpose is just satisfy the lockdep_assert_held() > check in intel_context_mark_active(). The other problem with disabling > interrupts is that on PREEMPT_RT interrupts are also disabled which > leads to problems for instance later during memory allocation. Hmm commit message of d67739268cf0 ("drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe") makes it sound like parking can run with interrupts disabled already. I mean outside of the irq disable hack in here. I don't see it possible though, both due might_lock in intel_wakeref_put and GFP_NOWAIT in switch_to_kernel_context. So I will assume that commit message refers to an earlier state of the code base. So the approach in this patch looks good to me. > Add a CONTEXT_IS_PARKED bit to intel_engine_cs and set_bit/clear_bit it > instead of mutex_acquire/mutex_release. Use test_bit in the two > identified spots which relied on the lockdep annotation. > > Cc: Peter Zijlstra > Signed-off-by: Sebastian Andrzej Siewior > --- > drivers/gpu/drm/i915/gt/intel_context.h | 3 +- > drivers/gpu/drm/i915/gt/intel_context_types.h | 1 > drivers/gpu/drm/i915/gt/intel_engine_pm.c | 38 +------------------------- > drivers/gpu/drm/i915/i915_request.h | 3 +- > 4 files changed, 7 insertions(+), 38 deletions(-) > > --- a/drivers/gpu/drm/i915/gt/intel_context.h > +++ b/drivers/gpu/drm/i915/gt/intel_context.h > @@ -211,7 +211,8 @@ static inline void intel_context_enter(s > > static inline void intel_context_mark_active(struct intel_context *ce) > { > - lockdep_assert_held(&ce->timeline->mutex); > + lockdep_assert(lockdep_is_held(&ce->timeline->mutex) || > + test_bit(CONTEXT_IS_PARKED, &ce->flags)); > ++ce->active_count; > } > > --- a/drivers/gpu/drm/i915/gt/intel_context_types.h > +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h > @@ -118,6 +118,7 @@ struct intel_context { > #define CONTEXT_LRCA_DIRTY 9 > #define CONTEXT_GUC_INIT 10 > #define CONTEXT_PERMA_PIN 11 > +#define CONTEXT_IS_PARKED 12 Pedantic comment is that semantics of the bit flag suggest it should be name CONTEXT_IS_PARKING, or along those lines. Since the flag gets clear as soon as the parking completes. I'd suggest doing that change for the self-documenting benefit. Regards, Tvrtko > > struct { > u64 timeout_us; > --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c > +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c > @@ -80,39 +80,6 @@ static int __engine_unpark(struct intel_ > return 0; > } > > -#if IS_ENABLED(CONFIG_LOCKDEP) > - > -static unsigned long __timeline_mark_lock(struct intel_context *ce) > -{ > - unsigned long flags; > - > - local_irq_save(flags); > - mutex_acquire(&ce->timeline->mutex.dep_map, 2, 0, _THIS_IP_); > - > - return flags; > -} > - > -static void __timeline_mark_unlock(struct intel_context *ce, > - unsigned long flags) > -{ > - mutex_release(&ce->timeline->mutex.dep_map, _THIS_IP_); > - local_irq_restore(flags); > -} > - > -#else > - > -static unsigned long __timeline_mark_lock(struct intel_context *ce) > -{ > - return 0; > -} > - > -static void __timeline_mark_unlock(struct intel_context *ce, > - unsigned long flags) > -{ > -} > - > -#endif /* !IS_ENABLED(CONFIG_LOCKDEP) */ > - > static void duration(struct dma_fence *fence, struct dma_fence_cb *cb) > { > struct i915_request *rq = to_request(fence); > @@ -159,7 +126,6 @@ static bool switch_to_kernel_context(str > { > struct intel_context *ce = engine->kernel_context; > struct i915_request *rq; > - unsigned long flags; > bool result = true; > > /* > @@ -214,7 +180,7 @@ static bool switch_to_kernel_context(str > * engine->wakeref.count, we may see the request completion and retire > * it causing an underflow of the engine->wakeref. > */ > - flags = __timeline_mark_lock(ce); > + set_bit(CONTEXT_IS_PARKED, &ce->flags); > GEM_BUG_ON(atomic_read(&ce->timeline->active_count) < 0); > > rq = __i915_request_create(ce, GFP_NOWAIT); > @@ -246,7 +212,7 @@ static bool switch_to_kernel_context(str > > result = false; > out_unlock: > - __timeline_mark_unlock(ce, flags); > + clear_bit(CONTEXT_IS_PARKED, &ce->flags); > return result; > } > > --- a/drivers/gpu/drm/i915/i915_request.h > +++ b/drivers/gpu/drm/i915/i915_request.h > @@ -642,7 +642,8 @@ i915_request_timeline(const struct i915_ > { > /* Valid only while the request is being constructed (or retired). */ > return rcu_dereference_protected(rq->timeline, > - lockdep_is_held(&rcu_access_pointer(rq->timeline)->mutex)); > + lockdep_is_held(&rcu_access_pointer(rq->timeline)->mutex) || > + test_bit(CONTEXT_IS_PARKED, &rq->context->flags)); > } > > static inline struct i915_gem_context * >