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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 C5D8FC2BB85 for ; Sat, 11 Apr 2020 12:18:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9FC942084D for ; Sat, 11 Apr 2020 12:18:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607514; bh=cnfW//iFPTjHMwCTSZLNmYBO4X0mI7EXj0oDE+xuzDY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=qmmwYxKl4ALEslYuQ2aHE1AmqClxtX5Q6MBazXUqDqIX9RTt7jasEkGiH91mlNkWd zdsrXA4tPbruoBLOH9EBsgQ+t612KxAGSHYU9+d3jBP2HZKIo8Iz5xqCAjjLCsGmby +768OTk5e/QF1z1WFzIP65IO1rkeJdTdxpMDT6Iw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728638AbgDKMSc (ORCPT ); Sat, 11 Apr 2020 08:18:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:53358 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728005AbgDKMS0 (ORCPT ); Sat, 11 Apr 2020 08:18:26 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6006220673; Sat, 11 Apr 2020 12:18:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607505; bh=cnfW//iFPTjHMwCTSZLNmYBO4X0mI7EXj0oDE+xuzDY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k8xWH84QxGxfCgo72P+XhhzAwuygmZNfzcLYu7UZdqnt9vbdIIxy6j+x+1SEFaPY4 lVDRNyDP16+dpKjH32sDC6qoSpkfWQHuMR7MHUcZoCnSnujHn4ne1apSLDzFL8hGCu fDzLXYz+PWzXCMBdywOS6Ac+hAPK/NnYNHQI+JVI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Sultan Alsawaf Subject: [PATCH 5.4 40/41] drm/i915: Fix ref->mutex deadlock in i915_active_wait() Date: Sat, 11 Apr 2020 14:09:49 +0200 Message-Id: <20200411115507.029644194@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200411115504.124035693@linuxfoundation.org> References: <20200411115504.124035693@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Sultan Alsawaf The following deadlock exists in i915_active_wait() due to a double lock on ref->mutex (call chain listed in order from top to bottom): i915_active_wait(); mutex_lock_interruptible(&ref->mutex); <-- ref->mutex first acquired i915_active_request_retire(); node_retire(); active_retire(); mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); <-- DEADLOCK Fix the deadlock by skipping the second ref->mutex lock when active_retire() is called through i915_active_request_retire(). Note that this bug only affects 5.4 and has since been fixed in 5.5. Normally, a backport of the fix from 5.5 would be in order, but the patch set that fixes this deadlock involves massive changes that are neither feasible nor desirable for backporting [1][2][3]. Therefore, this small patch was made to address the deadlock specifically for 5.4. [1] 274cbf20fd10 ("drm/i915: Push the i915_active.retire into a worker") [2] 093b92287363 ("drm/i915: Split i915_active.mutex into an irq-safe spinlock for the rbtree") [3] 750bde2fd4ff ("drm/i915: Serialise with remote retirement") Fixes: 12c255b5dad1 ("drm/i915: Provide an i915_active.acquire callback") Cc: # 5.4.x Signed-off-by: Sultan Alsawaf Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/i915/i915_active.c | 29 +++++++++++++++++++---------- drivers/gpu/drm/i915/i915_active.h | 4 ++-- 2 files changed, 21 insertions(+), 12 deletions(-) --- a/drivers/gpu/drm/i915/i915_active.c +++ b/drivers/gpu/drm/i915/i915_active.c @@ -121,7 +121,7 @@ static inline void debug_active_assert(s #endif static void -__active_retire(struct i915_active *ref) +__active_retire(struct i915_active *ref, bool lock) { struct active_node *it, *n; struct rb_root root; @@ -138,7 +138,8 @@ __active_retire(struct i915_active *ref) retire = true; } - mutex_unlock(&ref->mutex); + if (likely(lock)) + mutex_unlock(&ref->mutex); if (!retire) return; @@ -153,21 +154,28 @@ __active_retire(struct i915_active *ref) } static void -active_retire(struct i915_active *ref) +active_retire(struct i915_active *ref, bool lock) { GEM_BUG_ON(!atomic_read(&ref->count)); if (atomic_add_unless(&ref->count, -1, 1)) return; /* One active may be flushed from inside the acquire of another */ - mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); - __active_retire(ref); + if (likely(lock)) + mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); + __active_retire(ref, lock); } static void node_retire(struct i915_active_request *base, struct i915_request *rq) { - active_retire(node_from_active(base)->ref); + active_retire(node_from_active(base)->ref, true); +} + +static void +node_retire_nolock(struct i915_active_request *base, struct i915_request *rq) +{ + active_retire(node_from_active(base)->ref, false); } static struct i915_active_request * @@ -364,7 +372,7 @@ int i915_active_acquire(struct i915_acti void i915_active_release(struct i915_active *ref) { debug_active_assert(ref); - active_retire(ref); + active_retire(ref, true); } static void __active_ungrab(struct i915_active *ref) @@ -391,7 +399,7 @@ void i915_active_ungrab(struct i915_acti { GEM_BUG_ON(!test_bit(I915_ACTIVE_GRAB_BIT, &ref->flags)); - active_retire(ref); + active_retire(ref, true); __active_ungrab(ref); } @@ -421,12 +429,13 @@ int i915_active_wait(struct i915_active break; } - err = i915_active_request_retire(&it->base, BKL(ref)); + err = i915_active_request_retire(&it->base, BKL(ref), + node_retire_nolock); if (err) break; } - __active_retire(ref); + __active_retire(ref, true); if (err) return err; --- a/drivers/gpu/drm/i915/i915_active.h +++ b/drivers/gpu/drm/i915/i915_active.h @@ -309,7 +309,7 @@ i915_active_request_isset(const struct i */ static inline int __must_check i915_active_request_retire(struct i915_active_request *active, - struct mutex *mutex) + struct mutex *mutex, i915_active_retire_fn retire) { struct i915_request *request; long ret; @@ -327,7 +327,7 @@ i915_active_request_retire(struct i915_a list_del_init(&active->link); RCU_INIT_POINTER(active->request, NULL); - active->retire(active, request); + retire(active, request); return 0; }