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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 0C3C6C433EF for ; Wed, 8 Sep 2021 18:31:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D970661078 for ; Wed, 8 Sep 2021 18:31:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349887AbhIHScJ (ORCPT ); Wed, 8 Sep 2021 14:32:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233322AbhIHScH (ORCPT ); Wed, 8 Sep 2021 14:32:07 -0400 Received: from mail-ed1-x52e.google.com (mail-ed1-x52e.google.com [IPv6:2a00:1450:4864:20::52e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18934C061575 for ; Wed, 8 Sep 2021 11:30:59 -0700 (PDT) Received: by mail-ed1-x52e.google.com with SMTP id s25so4248636edw.0 for ; Wed, 08 Sep 2021 11:30:59 -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:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=/Qn6ettxHUUoxqY83dg+ur8SjU1z9HvqkiJi94oBfho=; b=WxFpfRLNjaZpO/2CuP+mTre5GuaHvTQMhYzbjqTPagPHEXTcvsj6iG8jwEamgYQPxV 3lqRjPv3oQ0OYD4pgcWC3IuoV7ySuoUq2b8K5MVqTNIc55GfKCotJatBofjrVUln5ecO XrQBt7fQKm4DXqtYcbTWdzcbVtTFV2kYPG458= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=/Qn6ettxHUUoxqY83dg+ur8SjU1z9HvqkiJi94oBfho=; b=YST7ywhm2K4DPSjGyvA7TzjirY7pFnnLYVlopBS/s3H5t/PwTlmA3/G5WD7ael5deJ +rMveflacqliDGCCZY0oasyCKbTbtxmxGomHmMCfgh9KJPmd0s06jHdGnGiQOGvrcvmg +uAufz2l4ejEjyi0GiY66w80EVGclO/4hdI/ScDzPZtOpFAo7b/6gWSfvJuOOc4eJ5qx 9yBNt8RUTplqizFZTi6kvRt7T+3lpSD71Of4dUlObRHlRRW2Qssf0+6YiVbvPPhxq9WF EOnieNt4i/NCr9DNGIGvSInDUgHYoEA4SoAm+CgHWs7LVBS2NUzwNgNCyrbDaX5EheP0 ZJeg== X-Gm-Message-State: AOAM530KywOmfdiq/q0vag8C6xn5+O2VYqZatV7J1ALtqrXJnEDhpAC1 siCEBk3PZ7I05f63HWZtX/cQCg== X-Google-Smtp-Source: ABdhPJzfI6Dt3rToBuXWwhqleGZ3105bWeKsWetnzWu6+M9Zwc3CxKRDDbnDMVWO6Xp6hXQxmkopqw== X-Received: by 2002:aa7:d40b:: with SMTP id z11mr5374364edq.224.1631125857634; Wed, 08 Sep 2021 11:30:57 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id p8sm1402262ejo.2.2021.09.08.11.30.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Sep 2021 11:30:56 -0700 (PDT) Date: Wed, 8 Sep 2021 20:30:54 +0200 From: Daniel Vetter To: Peter Zijlstra Cc: Maarten Lankhorst , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Liam Girdwood , Mark Brown , linux-kernel@vger.kernel.org Subject: Re: [PATCH] kernel/locking: Add context to ww_mutex_trylock. Message-ID: Mail-Followup-To: Peter Zijlstra , Maarten Lankhorst , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Liam Girdwood , Mark Brown , linux-kernel@vger.kernel.org References: <20210907132044.157225-1-maarten.lankhorst@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.10.0-8-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 08, 2021 at 12:14:23PM +0200, Peter Zijlstra wrote: > On Tue, Sep 07, 2021 at 03:20:44PM +0200, Maarten Lankhorst wrote: > > i915 will soon gain an eviction path that trylock a whole lot of locks > > for eviction, getting dmesg failures like below: > > > > BUG: MAX_LOCK_DEPTH too low! > > turning off the locking correctness validator. > > depth: 48 max: 48! > > 48 locks held by i915_selftest/5776: > > #0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160 > > #1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915] > > #2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915] > > #3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915] > > #4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > > #5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > > ... > > #46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > > #47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] > > INFO: lockdep is turned off. > > > As an intermediate solution, add an acquire context to ww_mutex_trylock, > > which allows us to do proper nesting annotations on the trylocks, making > > the above lockdep splat disappear. > > Fair enough I suppose. What's maybe missing from the commit message - we'll probably use this for ttm too eventually - even when we add full ww_mutex locking we'll still have the trylock fastpath. This is because we have a lock inversion against list locks in these eviction paths, and the slow path unroll to drop that list lock is a bit nasty (and defintely expensive). iow even long term this here is needed in some form I think. -Daniel > > > +/** > > + * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context > > + * @lock: mutex to lock > > + * @ctx: optional w/w acquire context > > + * > > + * Trylocks a mutex with the optional acquire context; no deadlock detection is > > + * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise. > > + * > > + * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is > > + * specified, -EALREADY and -EDEADLK handling may happen in calls to ww_mutex_lock. > > + * > > + * A mutex acquired with this function must be released with ww_mutex_unlock. > > + */ > > +int __sched > > +ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ctx) > > +{ > > + bool locked; > > + > > + if (!ctx) > > + return mutex_trylock(&ww->base); > > + > > +#ifdef CONFIG_DEBUG_MUTEXES > > + DEBUG_LOCKS_WARN_ON(ww->base.magic != &ww->base); > > +#endif > > + > > + preempt_disable(); > > + locked = __mutex_trylock(&ww->base); > > + > > + if (locked) { > > + ww_mutex_set_context_fastpath(ww, ctx); > > + mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ctx->dep_map, _RET_IP_); > > + } > > + preempt_enable(); > > + > > + return locked; > > +} > > +EXPORT_SYMBOL(ww_mutex_trylock); > > You'll need a similar hunk in ww_rt_mutex.c -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch