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SubjectRe: [PATCH] drm: qxl: ratelimit pr_info message, reduce log spamming
Hi Colin,

On 12 September 2017 at 10:45, Colin King <colin.king@canonical.com> wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> Simply mmap'ing /dev/dri/card0 repeatedly will spam the kernel
> log with qxl_mmap information messages. The following example code
> illustrates this:
>
> int main(void)
> {
> int fd = open("/dev/dri/card0", O_RDONLY);
> if (fd == -1)
> err(1, "open failed");
>
> for (;;) {
> void *m = mmap(NULL, 4096, PROT_READ,
> MAP_SHARED, fd, 0);
> if (m != MAP_FAILED)
> munmap(m, 4096);
> }
> }
>
> Reduce the spamming by ratelimiting the pr_info messages.
>
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
> drivers/gpu/drm/qxl/qxl_ttm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/qxl/qxl_ttm.c b/drivers/gpu/drm/qxl/qxl_ttm.c
> index 7ecf8a4b9fe6..6502e699f462 100644
> --- a/drivers/gpu/drm/qxl/qxl_ttm.c
> +++ b/drivers/gpu/drm/qxl/qxl_ttm.c
> @@ -124,7 +124,7 @@ int qxl_mmap(struct file *filp, struct vm_area_struct *vma)
> int r;
>
> if (unlikely(vma->vm_pgoff < DRM_FILE_PAGE_OFFSET)) {
> - pr_info("%s: vma->vm_pgoff (%ld) < DRM_FILE_PAGE_OFFSET\n",
> + pr_info_ratelimited("%s: vma->vm_pgoff (%ld) < DRM_FILE_PAGE_OFFSET\n",
Quick grep suggests that only qxl and vmwgfx produce any output in
this case, likely for the reasons you mentioned.

That said, I'm not sure how useful the information is - perhaps it's
better to drop it all together? Regardless of the route taken, vmwgfx
could use a similar fix.

HTH
Emil

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