linux-kernel - Re: [Intel-gfx] [PATCH 3/4] drm/ttm: Don't leak a resource on eviction error

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Date:   Thu, 22 Jun 2023 16:48:55 +0200
From:   Christian König <christian.koenig@....com>
To:     Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        Andi Shyti <andi.shyti@...ux.intel.com>
Cc:     intel-xe@...ts.freedesktop.org,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Huang Rui <ray.huang@....com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 3/4] drm/ttm: Don't leak a resource on
 eviction error



Am 22.06.23 um 16:08 schrieb Thomas Hellström:
>
> On 6/22/23 15:55, Andi Shyti wrote:
>> Hi Thomas,
>>
>> On Thu, Jun 22, 2023 at 12:14:11PM +0200, Thomas Hellström wrote:
>>> On eviction errors other than -EMULTIHOP we were leaking a resource.
>>> Fix.
>>>
>>> Fixes: 403797925768 ("drm/ttm: Fix multihop assert on eviction.")
>>> Cc: Andrey Grodzovsky <andrey.grodzovsky@....com>
>>> Cc: Christian König <christian.koenig@....com>
>>> Cc: Christian Koenig <christian.koenig@....com>
>>> Cc: Huang Rui <ray.huang@....com>
>>> Cc: dri-devel@...ts.freedesktop.org
>>> Cc: <stable@...r.kernel.org> # v5.15+
>>> Signed-off-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
>>> ---
>>>   drivers/gpu/drm/ttm/ttm_bo.c | 16 ++++++++--------
>>>   1 file changed, 8 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c 
>>> b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index 615d30c4262d..89530f2a027f 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -462,14 +462,14 @@ static int ttm_bo_evict(struct 
>>> ttm_buffer_object *bo,
>>>       ret = ttm_bo_handle_move_mem(bo, evict_mem, true, ctx, &hop);
>>>       if (ret == -EMULTIHOP) {
>>>           ret = ttm_bo_bounce_temp_buffer(bo, &evict_mem, ctx, &hop);
>>> -        if (ret) {
>>> -            if (ret != -ERESTARTSYS && ret != -EINTR)
>>> -                pr_err("Buffer eviction failed\n");
>>> -            ttm_resource_free(bo, &evict_mem);
>>> -            goto out;
>>> -        }
>>> -        /* try and move to final place now. */
>>> -        goto bounce;
>>> +        if (!ret)
>>> +            /* try and move to final place now. */
>>> +            goto bounce;
>> As we are at this, can't we replace this with a while()? Goto's
>> used instead of a while loop are a fist in the eye...
>
> I'm completely OK with that. this patch already did away with one of 
> them. Let's hear Christian's opinion first, though.

I'm not a fan of that goto either, but could we somehow avoid the 
while(1) ? E.g. something like do { } while (!ret) after handling the 
multihop?

Christian.

>
> Thanks,
>
> Thomas
>
>
>
>
>
>>
>> It looks even better:
>>
>>     while (1) {
>>         ret = ttm_bo_handle_move_mem(bo, evict_mem, true, ctx, &hop);
>>         if (!ret)
>>             break;
>>
>>         if (ret == -EMULTIHOP)
>>             ret = ttm_bo_bounce_temp_buffer(bo, &evict_mem,
>>                             ctx, &hop);
>>
>>         /* try again */
>>         if (!ret)
>>             continue;
>>
>>         ttm_resource_free(bo, &evict_mem);
>>         if (ret != -ERESTARTSYS && ret != -EINTR)
>>             pr_err("Buffer eviction failed\n");
>>
>>         break;
>>     }
>>
>> Andi
>>
>>> +    }
>>> +    if (ret) {
>>> +        ttm_resource_free(bo, &evict_mem);
>>> +        if (ret != -ERESTARTSYS && ret != -EINTR)
>>> +            pr_err("Buffer eviction failed\n");
>>>       }
>>>   out:
>>>       return ret;
>>> -- 
>>> 2.40.1