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=-15.3 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,URIBL_BLOCKED, 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 6299FC07E95 for ; Tue, 20 Jul 2021 10:20:49 +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 9D1C86113B for ; Tue, 20 Jul 2021 10:20:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9D1C86113B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=daenzer.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 02B1189FDD; Tue, 20 Jul 2021 10:20:48 +0000 (UTC) Received: from netline-mail3.netline.ch (mail.netline.ch [148.251.143.180]) by gabe.freedesktop.org (Postfix) with ESMTP id 29E7089FC9 for ; Tue, 20 Jul 2021 10:20:46 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by netline-mail3.netline.ch (Postfix) with ESMTP id D1A4620201E; Tue, 20 Jul 2021 12:20:44 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at netline-mail3.netline.ch Received: from netline-mail3.netline.ch ([127.0.0.1]) by localhost (netline-mail3.netline.ch [127.0.0.1]) (amavisd-new, port 10024) with LMTP id OCS8MDNA7x9a; Tue, 20 Jul 2021 12:20:44 +0200 (CEST) Received: from thor (24.99.2.85.dynamic.wline.res.cust.swisscom.ch [85.2.99.24]) by netline-mail3.netline.ch (Postfix) with ESMTPA id 50A4820201D; Tue, 20 Jul 2021 12:20:44 +0200 (CEST) Received: from localhost ([::1]) by thor with esmtp (Exim 4.94.2) (envelope-from ) id 1m5mrj-000d4g-57; Tue, 20 Jul 2021 12:20:43 +0200 To: =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20210709120756.205856-1-christian.koenig@amd.com> From: =?UTF-8?Q?Michel_D=c3=a4nzer?= Subject: Re: [PATCH] dma-buf: fix and rework dma_buf_poll v6 Message-ID: Date: Tue, 20 Jul 2021 12:20:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210709120756.205856-1-christian.koenig@amd.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 8bit 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: , Cc: daniel.vetter@ffwll.ch, dri-devel@lists.freedesktop.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 2021-07-09 2:07 p.m., Christian König wrote: > Daniel pointed me towards this function and there are multiple obvious problems > in the implementation. > > First of all the retry loop is not working as intended. In general the retry > makes only sense if you grab the reference first and then check the sequence > values. > > Then we should always also wait for the exclusive fence. > > It's also good practice to keep the reference around when installing callbacks > to fences you don't own. > > And last the whole implementation was unnecessary complex and rather hard to > understand which could lead to probably unexpected behavior of the IOCTL. > > Fix all this by reworking the implementation from scratch. Dropping the > whole RCU approach and taking the lock instead. > > Only mildly tested and needs a thoughtful review of the code. > > v2: fix the reference counting as well > v3: keep the excl fence handling as is for stable > v4: back to testing all fences, drop RCU > v5: handle in and out separately > v6: add missing clear of events > > Signed-off-by: Christian König > CC: stable@vger.kernel.org > --- > drivers/dma-buf/dma-buf.c | 156 +++++++++++++++++--------------------- > include/linux/dma-buf.h | 2 +- > 2 files changed, 72 insertions(+), 86 deletions(-) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index eadd1eaa2fb5..39e1ef872829 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c [...] > > static __poll_t dma_buf_poll(struct file *file, poll_table *poll) > { > struct dma_buf *dmabuf; > struct dma_resv *resv; > - struct dma_resv_list *fobj; > - struct dma_fence *fence_excl; > + unsigned shared_count; > __poll_t events; > - unsigned shared_count, seq; > + int r, i; shared_count, r & i are unused with this patch. > + if (events & EPOLLOUT && !dma_buf_poll_shared(resv, dcb) && > + !dma_buf_poll_excl(resv, dcb)) > + /* No callback queued, wake up any other waiters */ > + dma_buf_poll_cb(NULL, &dcb->cb); > + else > + events &= ~EPOLLOUT; Something like this might be clearer: if (events & EPOLLOUT) { if (!dma_buf_poll_shared(resv, dcb) && !dma_buf_poll_excl(resv, dcb)) /* No callback queued, wake up any other waiters */ dma_buf_poll_cb(NULL, &dcb->cb); else events &= ~EPOLLOUT; } > + if (events & EPOLLIN && !dma_buf_poll_excl(resv, dcb)) > + /* No callback queued, wake up any other waiters */ > dma_buf_poll_cb(NULL, &dcb->cb); > + else > + events &= ~EPOLLIN; Similarly: if (events & EPOLLIN) { if (!dma_buf_poll_excl(resv, dcb)) /* No callback queued, wake up any other waiters */ dma_buf_poll_cb(NULL, &dcb->cb); else events &= ~EPOLLIN; } Other than that, looks good to me, can't say anything about the locking though. Haven't been able to test this yet, hopefully later this week. -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer