2017-09-12 09:45:54

by Colin King

Subject: [PATCH] drm: qxl: ratelimit pr_info message, reduce log spamming

From: Colin Ian King <[email protected]>

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 <[email protected]>
---
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",
__func__, vma->vm_pgoff);
return -EINVAL;
}
--
2.14.1

2017-09-12 14:02:10

by Emil Velikov

Subject: Re: [PATCH] drm: qxl: ratelimit pr_info message, reduce log spamming

Hi Colin,

On 12 September 2017 at 10:45, Colin King <[email protected]> wrote:
> From: Colin Ian King <[email protected]>
>
> 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 <[email protected]>
> ---
> 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

2017-09-12 14:09:53

by Dan Carpenter

Subject: Re: [PATCH] drm: qxl: ratelimit pr_info message, reduce log spamming

On Tue, Sep 12, 2017 at 03:02:04PM +0100, Emil Velikov wrote:
> That said, I'm not sure how useful the information is - perhaps it's
> better to drop it all together?

Or a WARN_ONCE().

regards,
dan carpenter

2017-09-12 14:22:01

by Gerd Hoffmann

Subject: Re: [PATCH] drm: qxl: ratelimit pr_info message, reduce log spamming

On Tue, 2017-09-12 at 17:09 +0300, Dan Carpenter wrote:
> On Tue, Sep 12, 2017 at 03:02:04PM +0100, Emil Velikov wrote:
> > That said, I'm not sure how useful the information is - perhaps
> > it's
> > better to drop it all together?
>
> Or a WARN_ONCE().

It's userspace calling into the driver with invalid parameters.

IMO we should never WARN_ONCE() on something userspace can trigger.

I'd suggest to just drop the message altogether, simply throwing EINVAL
at userspace is perfectly fine IMHO.

cheers,
Gerd