Re: [PATCH] drm/tegra: Prevent BOs from being freed during job submission

[Dmitry Osipenko <digetx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 11.08.2017 21:16, Dmitry Osipenko wrote:
> On 11.08.2017 20:59, Thierry Reding wrote:
>> From: Dmitry Osipenko <digetx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>
>> Since DRM IOCTL's are lockless, there is a chance that BOs could be
>> released while a job submission is in progress. To avoid that, keep the
>> GEM reference until the job has been pinned, part of which will be to
>> take another reference.
>>
>> Signed-off-by: Dmitry Osipenko <digetx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> Signed-off-by: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>> ---
>>  drivers/gpu/drm/tegra/drm.c | 42 +++++++++++++++++++++++++++++++++---------
>>  1 file changed, 33 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
>> index f01db33fa20f..e5d19e1c9bc8 100644
>> --- a/drivers/gpu/drm/tegra/drm.c
>> +++ b/drivers/gpu/drm/tegra/drm.c
>> @@ -320,8 +320,6 @@ host1x_bo_lookup(struct drm_file *file, u32 handle)
>>  	if (!gem)
>>  		return NULL;
>>  
>> -	drm_gem_object_unreference_unlocked(gem);
>> -
>>  	bo = to_tegra_bo(gem);
>>  	return &bo->base;
>>  }
>> @@ -410,8 +408,10 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  		(void __user *)(uintptr_t)args->waitchks;
>>  	struct drm_tegra_syncpt syncpt;
>>  	struct host1x *host1x = dev_get_drvdata(drm->dev->parent);
>> +	struct drm_gem_object **refs;
>>  	struct host1x_syncpt *sp;
>>  	struct host1x_job *job;
>> +	unsigned int num_refs;
>>  	int err;
>>  
>>  	/* We don't yet support other than one syncpt_incr struct per submit */
>> @@ -433,6 +433,26 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  	job->class = context->client->base.class;
>>  	job->serialize = true;
>>  
>> +	/*
>> +	 * Track referenced BOs so that they can be unreferenced after the
>> +	 * submission is complete.
>> +	 */
>> +	num_refs = num_cmdbufs + num_relocs * 2 + num_waitchks;
>> +
>> +	if (sizeof(*refs) * num_refs > ULONG_MAX) {
> 
> Thierry, since you've omitted (u64) here (comparing to the original patch), I
> think it should be better to write as:
> 
> 	if (num_refs > ULONG_MAX / sizeof(*refs)) {
> 
> To avoid integer overflow in the check.
> 

Moreover, this check isn't needed at all because it duplicates same checking
done by kmalloc_array().

>> +		err = -EINVAL;
>> +		goto fail;
>> +	}
>> +
>> +	refs = kmalloc_array(num_refs, sizeof(*refs), GFP_KERNEL);
>> +	if (!refs) {
>> +		err = -ENOMEM;
>> +		goto fail;
>> +	}
>> +
>> +	/* reuse as an iterator later */
>> +	num_refs = 0;
>> +
>>  	while (num_cmdbufs) {
>>  		struct drm_tegra_cmdbuf cmdbuf;
>>  		struct host1x_bo *bo;
>> @@ -461,6 +481,7 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  
>>  		offset = (u64)cmdbuf.offset + (u64)cmdbuf.words * sizeof(u32);
>>  		obj = host1x_to_tegra_bo(bo);
>> +		refs[num_refs++] = &obj->gem;
>>  
>>  		/*
>>  		 * Gather buffer base address must be 4-bytes aligned,
>> @@ -490,6 +511,7 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  
>>  		reloc = &job->relocarray[num_relocs];
>>  		obj = host1x_to_tegra_bo(reloc->cmdbuf.bo);
>> +		refs[num_refs++] = &obj->gem;
>>  
>>  		/*
>>  		 * The unaligned cmdbuf offset will cause an unaligned write
>> @@ -503,6 +525,7 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  		}
>>  
>>  		obj = host1x_to_tegra_bo(reloc->target.bo);
>> +		refs[num_refs++] = &obj->gem;
>>  
>>  		if (reloc->target.offset >= obj->gem.size) {
>>  			err = -EINVAL;
>> @@ -522,6 +545,7 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  			goto fail;
>>  
>>  		obj = host1x_to_tegra_bo(wait->bo);
>> +		refs[num_refs++] = &obj->gem;
>>  
>>  		/*
>>  		 * The unaligned offset will cause an unaligned write during
>> @@ -561,17 +585,17 @@ int tegra_drm_submit(struct tegra_drm_context *context,
>>  		goto fail;
>>  
>>  	err = host1x_job_submit(job);
>> -	if (err)
>> -		goto fail_submit;
>> +	if (err) {
>> +		host1x_job_unpin(job);
>> +		goto fail;
>> +	}
>>  
>>  	args->fence = job->syncpt_end;
>>  
>> -	host1x_job_put(job);
>> -	return 0;
>> -
>> -fail_submit:
>> -	host1x_job_unpin(job);
>>  fail:
>> +	while (num_refs--)
>> +		drm_gem_object_put_unlocked(refs[num_refs]);
>> +
>>  	host1x_job_put(job);
>>  	return err;
>>  }
>>
> 
> 


-- 
Dmitry