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SubjectRe: [PATCH v3 9/9] drm/tegra: Support context isolation
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On 2/19/22 20:35, Dmitry Osipenko wrote:
> 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.

This refcount is intended to be dropped from 'release_job', where it's
dropped if job->context is set, which it is from this path.

>
>> + }
>> +
>> /*
>> * 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.

And this drop is for the refcount implicitly added when allocating the
memory context through host1x_context_alloc; so these two places should
be independent.

Please elaborate if I missed something.

Thanks,
Mikko

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