[Intel-gfx] [PATCH 22/43] drm/i915: prevent division by zero when asking for chipset power

[Kenneth Graunke]

On 12/14/2011 04:57 AM, Daniel Vetter wrote:
> From: Eugeni Dodonov <eugeni.dodonov at intel.com>
> 
> This prevents an in-kernel division by zero which happens when we are
> asking for i915_chipset_val too quickly, or within a race condition
> between the power monitoring thread and userspace accesses via debugfs.
> 
> The issue can be reproduced easily via the following command:
> while ``; do cat /sys/kernel/debug/dri/0/i915_emon_status; done
> 
> This is particularly dangerous because it can be triggered by
> a non-privileged user by just reading the debugfs entry.
> 
> This issue was also found independently by Konstantin Belousov
> <kostikbel at gmail.com>, who proposed a similar patch.
> 
> Reported-by: Konstantin Belousov <kostikbel at gmail.com>
> Acked-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> Acked-by: Keith Packard <keithp at keithp.com>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_dma.c |   10 ++++++++++
>  drivers/gpu/drm/i915/i915_drv.h |    1 +
>  2 files changed, 11 insertions(+), 0 deletions(-)

This has been in drm-intel-fixes since December 8th.