From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752458AbaEOJVa (ORCPT ); Thu, 15 May 2014 05:21:30 -0400 Received: from pegasos-out.vodafone.de ([80.84.1.38]:55605 "EHLO pegasos-out.vodafone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbaEOJV2 (ORCPT ); Thu, 15 May 2014 05:21:28 -0400 X-Spam-Flag: NO X-Spam-Score: -0.045 Authentication-Results: rohrpostix2.prod.vfnet.de (amavisd-new); dkim=pass header.i=@vodafone.de X-DKIM: OpenDKIM Filter v2.6.8 pegasos-out.vodafone.de 9165566F5A6 X-DKIM: OpenDKIM Filter v2.0.2 smtp-04.vodafone.de 68FB3E4EA2 Message-ID: <53748702.6070606@vodafone.de> Date: Thu, 15 May 2014 11:21:06 +0200 From: =?ISO-8859-1?Q?Christian_K=F6nig?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Maarten Lankhorst , airlied@linux.ie CC: nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences References: <20140514145134.21163.32350.stgit@patser> <20140514145809.21163.64947.stgit@patser> <53738BCC.2070809@vodafone.de> <5374131D.4010906@canonical.com> In-Reply-To: <5374131D.4010906@canonical.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 15.05.2014 03:06, schrieb Maarten Lankhorst: > op 14-05-14 17:29, Christian König schreef: >>> + /* did fence get signaled after we enabled the sw irq? */ >>> + if >>> (atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq) >= >>> fence->seq) { >>> + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring); >>> + return false; >>> + } >>> + >>> + fence->fence_wake.flags = 0; >>> + fence->fence_wake.private = NULL; >>> + fence->fence_wake.func = radeon_fence_check_signaled; >>> + __add_wait_queue(&fence->rdev->fence_queue, &fence->fence_wake); >>> + fence_get(f); >> That looks like a race condition to me. The fence needs to be added >> to the wait queue before the check, not after. >> >> Apart from that the whole approach looks like a really bad idea to >> me. How for example is lockup detection supposed to happen with this? > It's not a race condition because fence_queue.lock is held when this > function is called. Ah, I see. That's also the reason why you moved the wake_up_all out of the processing function. > > Lockup's a bit of a weird problem, the changes wouldn't allow core ttm > code to handle the lockup any more, > but any driver specific wait code would still handle this. I did this > by design, because in future patches the wait > function may be called from outside of the radeon driver. The official > wait function takes a timeout parameter, > so lockups wouldn't be fatal if the timeout is set to something like > 30*HZ for example, it would still return > and report that the function timed out. Timeouts help with the detection of the lockup, but not at all with the handling of them. What we essentially need is a wait callback into the driver that is called in non atomic context without any locks held. This way we can block for the fence to become signaled with a timeout and can then also initiate the reset handling if necessary. The way you designed the interface now means that the driver never gets a chance to wait for the hardware to become idle and so never has the opportunity to the reset the whole thing. Christian. > > ~Maarten