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SubjectRe: [PATCH] drm/vmwgfx: remove DRM_ERROR message, stops log spamming
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On 12/09/17 18:42, Thomas Hellstrom wrote:
> Hi, Colin,
>
> On 09/12/2017 07:35 PM, Colin King wrote:
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> mmap'ing the device multiple times will spam the kernel log with the
>> DRM_ERROR message about illegal mmap'ing the old fifo space.
> How are you hitting this? Multiple mappings should be fine as long as
> mapping offsets are correct,
> so hitting this message should indicate that the user-space app is doing
> something seriously wrong, and
> having it present in the log should probably help more than it hurts.
>
> /Thomas

Good question. I hit similar issues with the drm qxl driver when
running some kernel regression tests with stress-ng [1]. I realize this
is an artificial test scenario so it is definitely not a typical
use-case, however, sync the illegal mmapping will return -EINVAL the
application will pick up that this is an error without the need of
spotting it in the kernel log. And a user space application can perform
many millions of these invalid mmaps causing kernel log spamming.

[1] http://kernel.ubuntu.com/~cking/stress-ng/

>
>
>
>> Since
>> the mmap'ing will fail with an -EINVAL there is no need to emit this
>> message, so just remove it.
>>
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>> drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c | 4 +---
>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> index e771091d2cd3..1e633c602fb1 100644
>> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
>> @@ -33,10 +33,8 @@ int vmw_mmap(struct file *filp, struct
>> vm_area_struct *vma)
>> struct drm_file *file_priv;
>> struct vmw_private *dev_priv;
>> - if (unlikely(vma->vm_pgoff < VMWGFX_FILE_PAGE_OFFSET)) {
>> - DRM_ERROR("Illegal attempt to mmap old fifo space.\n");
>> + if (unlikely(vma->vm_pgoff < VMWGFX_FILE_PAGE_OFFSET))
>> return -EINVAL;
>> - }
>> file_priv = filp->private_data;
>> dev_priv = vmw_priv(file_priv->minor->dev);
>
>

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