Re: [PATCH 2/2] drm/i915: Handle vm_mmap error during I915_GEM_MMAP ioctl with WC set

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Joonas Lahtinen (2019-01-07 08:56:56)
> Add err goto label and use it when VMA can't be established or changes
> underneath.
> 
> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")

Dubious. All it changes is one branch where the error is forced to
-ENOMEM.

> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index f1d594a53978..97cbc0e27e3e 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1738,6 +1738,9 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>         addr = vm_mmap(obj->base.filp, 0, args->size,
>                        PROT_READ | PROT_WRITE, MAP_SHARED,
>                        args->offset);
> +       if (IS_ERR((void *)addr))
> +               goto err;
> +
>         if (args->flags & I915_MMAP_WC) {
>                 struct mm_struct *mm = current->mm;
>                 struct vm_area_struct *vma;
> @@ -1753,17 +1756,22 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                 else
>                         addr = -ENOMEM;
>                 up_write(&mm->mmap_sem);
> +               if (IS_ERR((void *)addr))
> +                       goto err;

The issue still remains that we are returning having called vm_mmap and
leaving the vma intact. And we've established above that calling
vm_munmap() is a race.
-Chris