[PATCH] drm/i915/switcheroo: check for NULL before dereferencing

[Jani Nikula]

On Mon, 18 Aug 2025, Gustavo Sousa <gustavo.sousa at intel.com> wrote:
> Quoting Jani Nikula (2025-08-18 10:30:30-03:00)
>>On Mon, 18 Aug 2025, Gustavo Sousa <gustavo.sousa at intel.com> wrote:
>>> Quoting Jani Nikula (2025-08-18 04:16:05-03:00)
>>>>Both i915_switcheroo_set_state() and i915_switcheroo_can_switch() check
>>>>for i915 == NULL. Commit d2e184f8e16a ("drm/i915/switcheroo: pass
>>>>display to HAS_DISPLAY()") started dereferencing it before the NULL
>>>>check. Fix it.
>>>
>>> Hm... Did it? I think i915->display will only give you an invalid
>>> address when i915 is NULL, but I don't think any dereferencing will
>>> happen, because of the checks on i915.
>>
>>What would be the case for &i915->display, but not i915->display?
>
> Ah, right.
>
> Yeah, I got confused thinking this was the same as the old times when we
> stored display directly in the structure. In that case, we would use
> &i915->display and no dereferencing would happen.
>
> Now we store a pointer to the display in i915 and we need
> dereferencing in order to get the address.
>
> Sorry for the noise!

Good to clarify!

Thanks for the review, pushed to din.

BR,
Jani.



>
> --
> Gustavo Sousa
>
>>
>>>
>>> Anyways, playing it safe here is probably a good idea. I would just
>>> reword the commit message a bit. With that,
>>>
>>> Reviewed-by: Gustavo Sousa <gustavo.sousa at intel.com>
>>
>>Thanks.
>>
>>>
>>>>
>>>>Fixes: d2e184f8e16a ("drm/i915/switcheroo: pass display to HAS_DISPLAY()")
>>>>Reported-by: kernel test robot <lkp at intel.com>
>>>>Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
>>>>Closes: https://lore.kernel.org/r/202508160035.hmzuKiww-lkp@intel.com/
>>>>Cc: Gustavo Sousa <gustavo.sousa at intel.com>
>>>>Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>>>>---
>>>> drivers/gpu/drm/i915/i915_switcheroo.c | 4 ++--
>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>>diff --git a/drivers/gpu/drm/i915/i915_switcheroo.c b/drivers/gpu/drm/i915/i915_switcheroo.c
>>>>index 231d27497706..3a95a55b2e87 100644
>>>>--- a/drivers/gpu/drm/i915/i915_switcheroo.c
>>>>+++ b/drivers/gpu/drm/i915/i915_switcheroo.c
>>>>@@ -15,7 +15,7 @@ static void i915_switcheroo_set_state(struct pci_dev *pdev,
>>>>                                       enum vga_switcheroo_state state)
>>>> {
>>>>         struct drm_i915_private *i915 = pdev_to_i915(pdev);
>>>>-        struct intel_display *display = i915->display;
>>>>+        struct intel_display *display = i915 ? i915->display : NULL;
>>>>         pm_message_t pmm = { .event = PM_EVENT_SUSPEND };
>>>> 
>>>>         if (!i915) {
>>>>@@ -45,7 +45,7 @@ static void i915_switcheroo_set_state(struct pci_dev *pdev,
>>>> static bool i915_switcheroo_can_switch(struct pci_dev *pdev)
>>>> {
>>>>         struct drm_i915_private *i915 = pdev_to_i915(pdev);
>>>>-        struct intel_display *display = i915->display;
>>>>+        struct intel_display *display = i915 ? i915->display : NULL;
>>>> 
>>>>         /*
>>>>          * FIXME: open_count is protected by drm_global_mutex but that would lead to
>>>>-- 
>>>>2.47.2
>>>>
>>
>>-- 
>>Jani Nikula, Intel

-- 
Jani Nikula, Intel