linux-kernel - Re: [PATCH v3 9/9] drm/tegra: Support context isolation

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Date:   Sat, 19 Feb 2022 21:35:19 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Mikko Perttunen <mperttunen@...dia.com>, thierry.reding@...il.com,
        jonathanh@...dia.com, joro@...tes.org, will@...nel.org,
        robh+dt@...nel.org, robin.murphy@....com
Cc:     linux-tegra@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 9/9] drm/tegra: Support context isolation

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.