linux-kernel - Re: [PATCH] drm/ttm: fix error handling in ttm_bo_handle_move

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Date:   Wed, 16 Jun 2021 10:47:14 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Thomas Hellstr <C3@...nda>, B6@...nda,
        m <thomas.hellstrom@...ux.intel.com>,
        Huang Rui <ray.huang@....com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/ttm: fix error handling in ttm_bo_handle_move_mem()



Am 16.06.21 um 10:37 schrieb Dan Carpenter:
> On Wed, Jun 16, 2021 at 08:46:33AM +0200, Christian König wrote:
>> Sending the first message didn't worked, so let's try again.
>>
>> Am 16.06.21 um 08:30 schrieb Dan Carpenter:
>>> There are three bugs here:
>>> 1) We need to call unpopulate() if ttm_tt_populate() succeeds.
>>> 2) The "new_man = ttm_manager_type(bdev, bo->mem.mem_type);" assignment
>>>      was wrong and it was really assigning "new_mem = old_mem;".  There
>>>      is no need for this assignment anyway as we already have the value
>>>      for "new_mem".
>>> 3) The (!new_man->use_tt) condition is reversed.
>>>
>>> Fixes: ba4e7d973dd0 ("drm: Add the TTM GPU memory manager subsystem.")
>>> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>>> ---
>>> This is from reading the code and I can't swear that I have understood
>>> it correctly.  My nouveau driver is currently unusable and this patch
>>> has not helped.  But hopefully if I fix enough bugs eventually it will
>>> start to work.
>> Well NAK, the code previously looked quite well and you are breaking it now.
>>
>> What's the problem with nouveau?
>>
> The new Firefox seems to excersize nouveau more than the old one so
> when I start 10 firefox windows it just hangs the graphics.
>
> I've added debug code and it seems like the problem is that
> nv50_mem_new() is failing.

Sounds like it is running out of memory to me.

Do you have a dmesg?

>
>
>>>    drivers/gpu/drm/ttm/ttm_bo.c | 14 ++++++++------
>>>    1 file changed, 8 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index ebcffe794adb..72dde093f754 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -180,12 +180,12 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
>>>    		 */
>>>    		ret = ttm_tt_create(bo, old_man->use_tt);
>>>    		if (ret)
>>> -			goto out_err;
>>> +			return ret;
>>>    		if (mem->mem_type != TTM_PL_SYSTEM) {
>>>    			ret = ttm_tt_populate(bo->bdev, bo->ttm, ctx);
>>>    			if (ret)
>>> -				goto out_err;
>>> +				goto err_destroy;
>>>    		}
>>>    	}
>>> @@ -193,15 +193,17 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
>>>    	if (ret) {
>>>    		if (ret == -EMULTIHOP)
>>>    			return ret;
>>> -		goto out_err;
>>> +		goto err_unpopulate;
>>>    	}
>>>    	ctx->bytes_moved += bo->base.size;
>>>    	return 0;
>>> -out_err:
>>> -	new_man = ttm_manager_type(bdev, bo->mem.mem_type);
>> This here switches new and old manager. E.g. the new_man is now pointing to
>> the existing resource manager.
> Why not just use "old_man" instead of basically the equivalent to
> "new_man = old_man"?  Can the old_man change part way through the
> function?

Good question :)

I don't think that old_man could change and yes that would be much more 
easier to understand.

Regards,
Christian.

>
> regards,
> dan carpenter
>