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

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Message-ID: <ef5d91b8-c68b-5edc-d611-6a4dbf55c945@linux.intel.com>
Date:   Thu, 22 Jun 2023 19:03:56 +0200
From:   Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
To:     Christian König <christian.koenig@....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


On 6/22/23 16:48, Christian König wrote:
>
>
> 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?

I think the construct that makes it most obvious what's happening, 
although it needs two tests for -EMULTIHOP is something like

do {
....
    if (ret != -EMULTIHOP)
       break;
    ....
} while (ret ==-EMULTIHOP);

Will be out tomorrow, though, so I don't have time to respin before Monday.

/Thomas


>
> 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
>