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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 514BCECAAA1 for ; Tue, 6 Sep 2022 10:21:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239223AbiIFKVH (ORCPT ); Tue, 6 Sep 2022 06:21:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55862 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239162AbiIFKVB (ORCPT ); Tue, 6 Sep 2022 06:21:01 -0400 Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ACEDC5E555; Tue, 6 Sep 2022 03:20:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1662459658; x=1693995658; h=message-id:date:mime-version:subject:to:references:from: in-reply-to:content-transfer-encoding; bh=CADQZNK7sh3ishR6VlRXnxfJnl5BQfip+USboN2REBU=; b=n8ZYU+fZBJbSjWMgLyo6gGgKPfFl3tLcsN2g55Tjr8ZG9FNN2yJNEkyu m8xqm/3OoVNsoY7aMhJLSPz666g+iMcLhMZv5hiKT5LIWmlE4nCK5KZMF Q8wBn/+zV1yHb3G1/8WjAOIPyRf5AATNHzR43P2U+KadOCv1PTDEzD5PI xxEQIhxPouOXyOfzRX1Rqhs3pjoYnqWmgkEzgi5Yi7ObOeeHBNbNIV36G stZcXfa49jpgrycrACuDGL5KszhbfzUecjrbH5tMQrbdx3P+wsmLr4tbk NMdI8w8dHWpi5GVAq04b82RdLKEbhAoP5skbyjwhNVW+K28KaZNu7pAdq g==; X-IronPort-AV: E=McAfee;i="6500,9779,10461"; a="360507050" X-IronPort-AV: E=Sophos;i="5.93,293,1654585200"; d="scan'208";a="360507050" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Sep 2022 03:20:57 -0700 X-IronPort-AV: E=Sophos;i="5.93,293,1654585200"; d="scan'208";a="644115071" Received: from holmesda-mobl.ger.corp.intel.com (HELO [10.213.204.21]) ([10.213.204.21]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Sep 2022 03:20:53 -0700 Message-ID: Date: Tue, 6 Sep 2022 11:20:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 Subject: Re: [PATCH v2 4/4] dma-buf: Check status of enable-signaling bit on debug Content-Language: en-US To: =?UTF-8?Q?Christian_K=c3=b6nig?= , Arvind Yadav , andrey.grodzovsky@amd.com, shashank.sharma@amd.com, amaranath.somalapuram@amd.com, Arunpravin.PaneerSelvam@amd.com, sumit.semwal@linaro.org, gustavo@padovan.org, airlied@linux.ie, daniel@ffwll.ch, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org References: <20220905163502.4032-1-Arvind.Yadav@amd.com> <20220905163502.4032-5-Arvind.Yadav@amd.com> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/2022 09:39, Christian König wrote: > Am 05.09.22 um 18:35 schrieb Arvind Yadav: >> The core DMA-buf framework needs to enable signaling >> before the fence is signaled. The core DMA-buf framework >> can forget to enable signaling before the fence is signaled. > > This sentence is a bit confusing. I'm not a native speaker of English > either, but I suggest something like: > > "Fence signaling must be enable to make sure that the > dma_fence_is_signaled() function ever returns true." > >> To avoid this scenario on the debug kernel, check the >> DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT status bit before checking >> the signaling bit status to confirm that enable_signaling >> is enabled. > > This describes the implementation, but we should rather describe the > background of the change. The implementation should be obvious. > Something like this maybe: > > " > Since drivers and implementations sometimes mess this up enforce correct > behavior when DEBUG_WW_MUTEX_SLOWPATH is used during debugging. > > This should make any implementations bugs resulting in not signaled > fences much more obvious. > " I think I follow the idea but am not sure coupling (well "coupling".. not really, but cross-contaminating in a way) dma-fence.c with a foreign and effectively unrelated concept of a ww mutex is the best way. Instead, how about a dma-buf specific debug kconfig option? Condition would then be, according to my understanding of the rules and expectations, along the lines of: diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..147a9df2c9d0 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -428,6 +428,17 @@ dma_fence_is_signaled_locked(struct dma_fence *fence) static inline bool dma_fence_is_signaled(struct dma_fence *fence) { +#ifdef CONFIG_DEBUG_DMAFENCE + /* + * Implementations not providing the enable_signaling callback are + * required to always have signaling enabled or fences are not + * guaranteed to ever signal. + */ + if (!fence->ops->enable_signaling && + !test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) + return false; +#endif + if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) return true; Thoughts? Regards, Tvrtko > >> >> Signed-off-by: Arvind Yadav > > With the improved commit message this patch is Reviewed-by: Christian > König > > Regards, > Christian. > >> --- >> >> Changes in v1 : >> 1- Addressing Christian's comment to replace >> CONFIG_DEBUG_WW_MUTEX_SLOWPATH instead of CONFIG_DEBUG_FS. >> 2- As per Christian's comment moving this patch at last so >> The version of this patch is also changed and previously >> it was [PATCH 1/4] >> >> >> --- >>   include/linux/dma-fence.h | 5 +++++ >>   1 file changed, 5 insertions(+) >> >> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h >> index 775cdc0b4f24..ba1ddc14c5d4 100644 >> --- a/include/linux/dma-fence.h >> +++ b/include/linux/dma-fence.h >> @@ -428,6 +428,11 @@ dma_fence_is_signaled_locked(struct dma_fence >> *fence) >>   static inline bool >>   dma_fence_is_signaled(struct dma_fence *fence) >>   { >> +#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH >> +    if (!test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) >> +        return false; >> +#endif >> + >>       if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) >>           return true; >