Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <2b4dd244-f918-4d26-2322-00a0bb226ccf@gmail.com>
Date:   Sat, 19 Feb 2022 21:35:19 +0300
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [PATCH v3 9/9] drm/tegra: Support context isolation
Content-Language: en-US
To:     Mikko Perttunen <mperttunen@nvidia.com>, thierry.reding@gmail.com,
        jonathanh@nvidia.com, joro@8bytes.org, will@kernel.org,
        robh+dt@kernel.org, robin.murphy@arm.com
Cc:     linux-tegra@vger.kernel.org, dri-devel@lists.freedesktop.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20220218113952.3077606-1-mperttunen@nvidia.com>
 <20220218113952.3077606-10-mperttunen@nvidia.com>
From:   Dmitry Osipenko <digetx@gmail.com>
In-Reply-To: <20220218113952.3077606-10-mperttunen@nvidia.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

18.02.2022 14:39, Mikko Perttunen пишет:
> +	if (context->memory_context && context->client->ops->get_streamid_offset) {
            ^^^
> +		int offset = context->client->ops->get_streamid_offset(context->client);
> +
> +		if (offset >= 0) {
> +			job->context = context->memory_context;
> +			job->engine_streamid_offset = offset;
> +			host1x_context_get(job->context);
> +		}

You should bump refcount unconditionally or you'll get refcnt underflow
on put, when offset < 0.

> +	}
> +
>  	/*
>  	 * job_data is now part of job reference counting, so don't release
>  	 * it from here.
> diff --git a/drivers/gpu/drm/tegra/uapi.c b/drivers/gpu/drm/tegra/uapi.c
> index 9ab9179d2026..be33da54d12c 100644
> --- a/drivers/gpu/drm/tegra/uapi.c
> +++ b/drivers/gpu/drm/tegra/uapi.c
> @@ -33,6 +33,9 @@ static void tegra_drm_channel_context_close(struct tegra_drm_context *context)
>  	struct tegra_drm_mapping *mapping;
>  	unsigned long id;
>  
> +	if (context->memory_context)
> +		host1x_context_put(context->memory_context);

The "if (context->memory_context &&
context->client->ops->get_streamid_offset)" above doesn't match the "if
(context->memory_context)". You'll get refcount underflow.