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

[Gustavo Sousa]

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.

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>

>
>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
>