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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EDBEAC4320A for ; Tue, 31 Aug 2021 12:17:03 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id B1F236101B for ; Tue, 31 Aug 2021 12:17:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org B1F236101B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 105AE89930; Tue, 31 Aug 2021 12:17:02 +0000 (UTC) Received: from mail-wm1-x335.google.com (mail-wm1-x335.google.com [IPv6:2a00:1450:4864:20::335]) by gabe.freedesktop.org (Postfix) with ESMTPS id DEA5989930 for ; Tue, 31 Aug 2021 12:17:00 +0000 (UTC) Received: by mail-wm1-x335.google.com with SMTP id z9-20020a7bc149000000b002e8861aff59so1948633wmi.0 for ; Tue, 31 Aug 2021 05:17:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=T2lgE0IkIC7oFKkAT/qIaSVwEdEUqyyLmRFppoclZSo=; b=Eb7QDeaWoM6bBmmUStvfD2QhIlP+01ibpr4WntvGm5AIHEcuk7GDFyt8FuEBUr65pE +bsL1UzJCP23hDRPpBiVHC1jc3SkAGwj/2LwFNLjQ0zmfK6CYTPjlPSH9/+UKfpl5iYp cXcg+PVuuUVWyHhsS31/xWAlaWkv9sdhlv9q8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=T2lgE0IkIC7oFKkAT/qIaSVwEdEUqyyLmRFppoclZSo=; b=LDxtA1e3bBPbXXi2oVDoD9SiHIiqBI2t/yfPXx82VKPmBnQuEE5dUl5PzrMhhu5e1s +0yknMj2rPe+T+gHf+YTtLYHdCzZU8QSpOP7hu+Bim/2d3CdHdwIGNCtZPeGrMZDoA4J UJblaN2CmK8Un6g8Ym6ue+2jgkCwKRcDyd22u98fS0XOBfqDqVeUZrVuv7VY2sK1ihVv 8+KhYonwdSlolQCp73YxaSIw3R02QMAJNG+kNOFcUYkmwLgt7kcUP4EHTCSPtV/vdJca kEHh9pJ3IX9QjfbY5idAH0oq+/GkbrbJCWfmJJ5Ze1ZxeRdnCKxlqwHuOPl0/1i0OCAA fptg== X-Gm-Message-State: AOAM533+uzATeKcxLKGIzhaSsjCiW1o/CIuiwij5mBDEAUfw+PCJtDVS HRRzuwF9b4EoCU7ypcCoBlxX+w== X-Google-Smtp-Source: ABdhPJxzHOr7ZNp7C6tnbLP28xvXmxfJ85BH0pkjNwYF9iZdmV/1ZQPm5oUEc0eW8ASBJ6hixwKgdQ== X-Received: by 2002:a05:600c:a05:: with SMTP id z5mr3999335wmp.73.1630412219236; Tue, 31 Aug 2021 05:16:59 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id s7sm18293622wra.75.2021.08.31.05.16.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Aug 2021 05:16:58 -0700 (PDT) Date: Tue, 31 Aug 2021 14:16:56 +0200 From: Daniel Vetter To: Maarten Lankhorst Cc: Daniel Vetter , Intel Graphics Development , DRI Development , Daniel Vetter , Jon Bloomfield , Chris Wilson , Joonas Lahtinen , Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Matthew Auld , Lionel Landwerlin , Dave Airlie , Jason Ekstrand Subject: Re: [PATCH] drm/i915: Release i915_gem_context from a worker Message-ID: References: <20210813203033.3179400-1-daniel.vetter@ffwll.ch> <20210814104319.3226156-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: Linux phenom 5.10.0-8-amd64 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue, Aug 31, 2021 at 11:38:27AM +0200, Maarten Lankhorst wrote: > Op 14-08-2021 om 12:43 schreef Daniel Vetter: > > The only reason for this really is the i915_gem_engines->fence > > callback engines_notify(), which exists purely as a fairly funky > > reference counting scheme for that. Otherwise all other callers are > > from process context, and generally fairly benign locking context. > > > > Unfortunately untangling that requires some major surgery, and we have > > a few i915_gem_context reference counting bugs that need fixing, and > > they blow in the current hardirq calling context, so we need a > > stop-gap measure. > > > > Put a FIXME comment in when this should be removable again. > > > > v2: Fix mock_context(), noticed by intel-gfx-ci. > > > > Signed-off-by: Daniel Vetter > > Cc: Jon Bloomfield > > Cc: Chris Wilson > > Cc: Maarten Lankhorst > > Cc: Joonas Lahtinen > > Cc: Daniel Vetter > > Cc: "Thomas Hellström" > > Cc: Matthew Auld > > Cc: Lionel Landwerlin > > Cc: Dave Airlie > > Cc: Jason Ekstrand > > --- > > drivers/gpu/drm/i915/gem/i915_gem_context.c | 13 +++++++++++-- > > drivers/gpu/drm/i915/gem/i915_gem_context_types.h | 12 ++++++++++++ > > drivers/gpu/drm/i915/gem/selftests/mock_context.c | 1 + > > 3 files changed, 24 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c > > index fd169cf2f75a..051bc357ff65 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c > > @@ -986,9 +986,10 @@ static struct i915_gem_engines *user_engines(struct i915_gem_context *ctx, > > return err; > > } > > > > -void i915_gem_context_release(struct kref *ref) > > +static void i915_gem_context_release_work(struct work_struct *work) > > { > > - struct i915_gem_context *ctx = container_of(ref, typeof(*ctx), ref); > > + struct i915_gem_context *ctx = container_of(work, typeof(*ctx), > > + release_work); > > > > trace_i915_context_free(ctx); > > GEM_BUG_ON(!i915_gem_context_is_closed(ctx)); > > @@ -1002,6 +1003,13 @@ void i915_gem_context_release(struct kref *ref) > > kfree_rcu(ctx, rcu); > > } > > > > +void i915_gem_context_release(struct kref *ref) > > +{ > > + struct i915_gem_context *ctx = container_of(ref, typeof(*ctx), ref); > > + > > + queue_work(ctx->i915->wq, &ctx->release_work); > > +} > > + > > static inline struct i915_gem_engines * > > __context_engines_static(const struct i915_gem_context *ctx) > > { > > @@ -1303,6 +1311,7 @@ i915_gem_create_context(struct drm_i915_private *i915, > > ctx->sched = pc->sched; > > mutex_init(&ctx->mutex); > > INIT_LIST_HEAD(&ctx->link); > > + INIT_WORK(&ctx->release_work, i915_gem_context_release_work); > > > > spin_lock_init(&ctx->stale.lock); > > INIT_LIST_HEAD(&ctx->stale.engines); > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h > > index 94c03a97cb77..0c38789bd4a8 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h > > @@ -288,6 +288,18 @@ struct i915_gem_context { > > */ > > struct kref ref; > > > > + /** > > + * @release_work: > > + * > > + * Work item for deferred cleanup, since i915_gem_context_put() tends to > > + * be called from hardirq context. > > + * > > + * FIXME: The only real reason for this is &i915_gem_engines.fence, all > > + * other callers are from process context and need at most some mild > > + * shuffling to pull the i915_gem_context_put() call out of a spinlock. > > + */ > > + struct work_struct release_work; > > + > > /** > > * @rcu: rcu_head for deferred freeing. > > */ > > diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_context.c b/drivers/gpu/drm/i915/gem/selftests/mock_context.c > > index fee070df1c97..067d68a6fe4c 100644 > > --- a/drivers/gpu/drm/i915/gem/selftests/mock_context.c > > +++ b/drivers/gpu/drm/i915/gem/selftests/mock_context.c > > @@ -23,6 +23,7 @@ mock_context(struct drm_i915_private *i915, > > kref_init(&ctx->ref); > > INIT_LIST_HEAD(&ctx->link); > > ctx->i915 = i915; > > + INIT_WORK(&ctx->release_work, i915_gem_context_release_work); > > > > mutex_init(&ctx->mutex); > > > > ---- > Is the workqueue really needed? I'm not sure you could still race in > drm_syncobj_free when refcount is zero, so in that case removing locking > from _release would work as well as a workqueue. > > Something like below would keep the drm_sync_obj_put hardirq safe. > > I assume when freeing, the cb list is supposed to be empty, so I added a WARN_ON just to be sure, otherwise we should just tear down the list without locking too. > > This should be a better alternative for patch 1. This isn't enough, because the problem isn't just the syncobj put. It's also the i915_vm_put, and if we dercuify the intel_context stuff too, then there will be more intel_context_put on top. So we really need the worker here I think. Trying to make every _unpin() and _put() work from hardirq context with clever locking tricks is why the current code is so incomprehensible. Also vms are rare enough that we really don't care about some overhead/delay here. -Daniel > ----8<------- > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c > index c9a9d74f338c..9d561decd97e 100644 > --- a/drivers/gpu/drm/drm_syncobj.c > +++ b/drivers/gpu/drm/drm_syncobj.c > @@ -462,7 +462,13 @@ void drm_syncobj_free(struct kref *kref) > struct drm_syncobj *syncobj = container_of(kref, > struct drm_syncobj, > refcount); > - drm_syncobj_replace_fence(syncobj, NULL); > + struct dma_fence *old_fence; > + > + old_fence = rcu_dereference_protected(syncobj->fence, !kref_read(&syncobj->refcount)); > + dma_fence_put(old_fence); > + > + WARN_ON(!list_empty(&syncobj->cb_list)); > + > kfree(syncobj); > } > EXPORT_SYMBOL(drm_syncobj_free); > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch 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 X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5DBAC432BE for ; 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Tue, 31 Aug 2021 05:16:59 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id s7sm18293622wra.75.2021.08.31.05.16.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Aug 2021 05:16:58 -0700 (PDT) Date: Tue, 31 Aug 2021 14:16:56 +0200 From: Daniel Vetter To: Maarten Lankhorst Cc: Daniel Vetter , Intel Graphics Development , DRI Development , Daniel Vetter , Jon Bloomfield , Chris Wilson , Joonas Lahtinen , Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Matthew Auld , Lionel Landwerlin , Dave Airlie , Jason Ekstrand Message-ID: References: <20210813203033.3179400-1-daniel.vetter@ffwll.ch> <20210814104319.3226156-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: Linux phenom 5.10.0-8-amd64 Subject: Re: [Intel-gfx] [PATCH] drm/i915: Release i915_gem_context from a worker 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: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Tue, Aug 31, 2021 at 11:38:27AM +0200, Maarten Lankhorst wrote: > Op 14-08-2021 om 12:43 schreef Daniel Vetter: > > The only reason for this really is the i915_gem_engines->fence > > callback engines_notify(), which exists purely as a fairly funky > > reference counting scheme for that. Otherwise all other callers are > > from process context, and generally fairly benign locking context. > > > > Unfortunately untangling that requires some major surgery, and we have > > a few i915_gem_context reference counting bugs that need fixing, and > > they blow in the current hardirq calling context, so we need a > > stop-gap measure. > > > > Put a FIXME comment in when this should be removable again. > > > > v2: Fix mock_context(), noticed by intel-gfx-ci. > > > > Signed-off-by: Daniel Vetter > > Cc: Jon Bloomfield > > Cc: Chris Wilson > > Cc: Maarten Lankhorst > > Cc: Joonas Lahtinen > > Cc: Daniel Vetter > > Cc: "Thomas Hellström" > > Cc: Matthew Auld > > Cc: Lionel Landwerlin > > Cc: Dave Airlie > > Cc: Jason Ekstrand > > --- > > drivers/gpu/drm/i915/gem/i915_gem_context.c | 13 +++++++++++-- > > drivers/gpu/drm/i915/gem/i915_gem_context_types.h | 12 ++++++++++++ > > drivers/gpu/drm/i915/gem/selftests/mock_context.c | 1 + > > 3 files changed, 24 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c > > index fd169cf2f75a..051bc357ff65 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c > > @@ -986,9 +986,10 @@ static struct i915_gem_engines *user_engines(struct i915_gem_context *ctx, > > return err; > > } > > > > -void i915_gem_context_release(struct kref *ref) > > +static void i915_gem_context_release_work(struct work_struct *work) > > { > > - struct i915_gem_context *ctx = container_of(ref, typeof(*ctx), ref); > > + struct i915_gem_context *ctx = container_of(work, typeof(*ctx), > > + release_work); > > > > trace_i915_context_free(ctx); > > GEM_BUG_ON(!i915_gem_context_is_closed(ctx)); > > @@ -1002,6 +1003,13 @@ void i915_gem_context_release(struct kref *ref) > > kfree_rcu(ctx, rcu); > > } > > > > +void i915_gem_context_release(struct kref *ref) > > +{ > > + struct i915_gem_context *ctx = container_of(ref, typeof(*ctx), ref); > > + > > + queue_work(ctx->i915->wq, &ctx->release_work); > > +} > > + > > static inline struct i915_gem_engines * > > __context_engines_static(const struct i915_gem_context *ctx) > > { > > @@ -1303,6 +1311,7 @@ i915_gem_create_context(struct drm_i915_private *i915, > > ctx->sched = pc->sched; > > mutex_init(&ctx->mutex); > > INIT_LIST_HEAD(&ctx->link); > > + INIT_WORK(&ctx->release_work, i915_gem_context_release_work); > > > > spin_lock_init(&ctx->stale.lock); > > INIT_LIST_HEAD(&ctx->stale.engines); > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h > > index 94c03a97cb77..0c38789bd4a8 100644 > > --- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h > > @@ -288,6 +288,18 @@ struct i915_gem_context { > > */ > > struct kref ref; > > > > + /** > > + * @release_work: > > + * > > + * Work item for deferred cleanup, since i915_gem_context_put() tends to > > + * be called from hardirq context. > > + * > > + * FIXME: The only real reason for this is &i915_gem_engines.fence, all > > + * other callers are from process context and need at most some mild > > + * shuffling to pull the i915_gem_context_put() call out of a spinlock. > > + */ > > + struct work_struct release_work; > > + > > /** > > * @rcu: rcu_head for deferred freeing. > > */ > > diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_context.c b/drivers/gpu/drm/i915/gem/selftests/mock_context.c > > index fee070df1c97..067d68a6fe4c 100644 > > --- a/drivers/gpu/drm/i915/gem/selftests/mock_context.c > > +++ b/drivers/gpu/drm/i915/gem/selftests/mock_context.c > > @@ -23,6 +23,7 @@ mock_context(struct drm_i915_private *i915, > > kref_init(&ctx->ref); > > INIT_LIST_HEAD(&ctx->link); > > ctx->i915 = i915; > > + INIT_WORK(&ctx->release_work, i915_gem_context_release_work); > > > > mutex_init(&ctx->mutex); > > > > ---- > Is the workqueue really needed? I'm not sure you could still race in > drm_syncobj_free when refcount is zero, so in that case removing locking > from _release would work as well as a workqueue. > > Something like below would keep the drm_sync_obj_put hardirq safe. > > I assume when freeing, the cb list is supposed to be empty, so I added a WARN_ON just to be sure, otherwise we should just tear down the list without locking too. > > This should be a better alternative for patch 1. This isn't enough, because the problem isn't just the syncobj put. It's also the i915_vm_put, and if we dercuify the intel_context stuff too, then there will be more intel_context_put on top. So we really need the worker here I think. Trying to make every _unpin() and _put() work from hardirq context with clever locking tricks is why the current code is so incomprehensible. Also vms are rare enough that we really don't care about some overhead/delay here. -Daniel > ----8<------- > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c > index c9a9d74f338c..9d561decd97e 100644 > --- a/drivers/gpu/drm/drm_syncobj.c > +++ b/drivers/gpu/drm/drm_syncobj.c > @@ -462,7 +462,13 @@ void drm_syncobj_free(struct kref *kref) > struct drm_syncobj *syncobj = container_of(kref, > struct drm_syncobj, > refcount); > - drm_syncobj_replace_fence(syncobj, NULL); > + struct dma_fence *old_fence; > + > + old_fence = rcu_dereference_protected(syncobj->fence, !kref_read(&syncobj->refcount)); > + dma_fence_put(old_fence); > + > + WARN_ON(!list_empty(&syncobj->cb_list)); > + > kfree(syncobj); > } > EXPORT_SYMBOL(drm_syncobj_free); > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch