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=-16.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 773FBC432BE for ; Tue, 31 Aug 2021 09:38:15 +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 31D0A60F6B for ; Tue, 31 Aug 2021 09:38:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 31D0A60F6B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com 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 A0A1A89A08; Tue, 31 Aug 2021 09:38:14 +0000 (UTC) Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9223989A08; Tue, 31 Aug 2021 09:38:13 +0000 (UTC) X-IronPort-AV: E=McAfee;i="6200,9189,10092"; a="240690631" X-IronPort-AV: E=Sophos;i="5.84,366,1620716400"; d="scan'208";a="240690631" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Aug 2021 02:38:13 -0700 X-IronPort-AV: E=Sophos;i="5.84,366,1620716400"; d="scan'208";a="531027886" Received: from wenqitan-mobl1.ger.corp.intel.com (HELO [10.252.59.180]) ([10.252.59.180]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 31 Aug 2021 02:38:10 -0700 To: Daniel Vetter , Intel Graphics Development Cc: DRI Development , Daniel Vetter , Jon Bloomfield , Chris Wilson , Joonas Lahtinen , =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= , Matthew Auld , Lionel Landwerlin , Dave Airlie , Jason Ekstrand References: <20210813203033.3179400-1-daniel.vetter@ffwll.ch> <20210814104319.3226156-1-daniel.vetter@ffwll.ch> From: Maarten Lankhorst Message-ID: Date: Tue, 31 Aug 2021 11:38:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210814104319.3226156-1-daniel.vetter@ffwll.ch> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US 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" 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. ----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);