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=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 63851C33CB2 for ; Wed, 29 Jan 2020 09:33:30 +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 3F3EC20716 for ; Wed, 29 Jan 2020 09:33:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F3EC20716 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=chris-wilson.co.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A92FB6E267; Wed, 29 Jan 2020 09:33:29 +0000 (UTC) Received: from fireflyinternet.com (mail.fireflyinternet.com [109.228.58.192]) by gabe.freedesktop.org (Postfix) with ESMTPS id 850676E267 for ; Wed, 29 Jan 2020 09:33:27 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from localhost (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP (TLS) id 20044717-1500050 for multiple; Wed, 29 Jan 2020 09:33:23 +0000 MIME-Version: 1.0 From: Chris Wilson User-Agent: alot/0.6 To: Mika Kuoppala , intel-gfx@lists.freedesktop.org References: <20200128171614.3845825-1-chris@chris-wilson.co.uk> <87k15aa9vc.fsf@gaia.fi.intel.com> In-Reply-To: <87k15aa9vc.fsf@gaia.fi.intel.com> Message-ID: <158029040255.10244.7113266483710281976@skylake-alporthouse-com> Date: Wed, 29 Jan 2020 09:33:22 +0000 Subject: Re: [Intel-gfx] [PATCH] drm/i915/execlist: Mark up racy read of execlists->pending[0] 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Quoting Mika Kuoppala (2020-01-29 09:29:43) > Chris Wilson writes: > > > We write to execlists->pending[0] in process_csb() to acknowledge the > > completion of the ESLP update, outside of the main spinlock. When we > > check the current status of the previous submission in > > __execlists_submission_tasklet() we should therefore use READ_ONCE() to > > reflect and document the unsynchronized read. > > > > Signed-off-by: Chris Wilson > > Cc: Tvrtko Ursulin > > --- > > drivers/gpu/drm/i915/gt/intel_lrc.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c > > index cf6c43bd540a..058484958e87 100644 > > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c > > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c > > @@ -2347,7 +2347,7 @@ static void process_csb(struct intel_engine_cs *engine) > > static void __execlists_submission_tasklet(struct intel_engine_cs *const engine) > > { > > lockdep_assert_held(&engine->active.lock); > > - if (!engine->execlists.pending[0]) { > > + if (!READ_ONCE(engine->execlists.pending[0])) { > > With same token, should we also include assert_pending_invalid() > read of pending with READ_ONCE? That happens on the control paths, so the state of pending[] at that point should be static (and the compiler can be left to its own devices). -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx