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SubjectRe: [PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed
friendly ping.

I am not even myself completely convinced that this is the correct
patch and it might just workaround some issues, but list_debug.c does
check if a list was already deleted and throws an error if it was and
this patch indeed fixes this one issue as multiple threads could enter
__i915_vma_remove_closed on the same vma.


On Wed, Apr 20, 2022 at 11:57 AM Karol Herbst <kherbst@redhat.com> wrote:
>
> i915_vma_reopen checked if the vma is closed before without taking the
> lock. So multiple threads could attempt removing the vma.
>
> Instead the lock needs to be taken before actually checking.
>
> v2: move struct declaration
>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: intel-gfx@lists.freedesktop.org
> Cc: dri-devel@lists.freedesktop.org
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
> Signed-off-by: Karol Herbst <kherbst@redhat.com>
> ---
> drivers/gpu/drm/i915/i915_vma.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 162e8d83691b..2efdad2b43fa 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -1615,17 +1615,17 @@ void i915_vma_close(struct i915_vma *vma)
>
> static void __i915_vma_remove_closed(struct i915_vma *vma)
> {
> - struct intel_gt *gt = vma->vm->gt;
> -
> - spin_lock_irq(&gt->closed_lock);
> list_del_init(&vma->closed_link);
> - spin_unlock_irq(&gt->closed_lock);
> }
>
> void i915_vma_reopen(struct i915_vma *vma)
> {
> + struct intel_gt *gt = vma->vm->gt;
> +
> + spin_lock_irq(&gt->closed_lock);
> if (i915_vma_is_closed(vma))
> __i915_vma_remove_closed(vma);
> + spin_unlock_irq(&gt->closed_lock);
> }
>
> static void force_unbind(struct i915_vma *vma)
> @@ -1641,6 +1641,7 @@ static void force_unbind(struct i915_vma *vma)
> static void release_references(struct i915_vma *vma, bool vm_ddestroy)
> {
> struct drm_i915_gem_object *obj = vma->obj;
> + struct intel_gt *gt = vma->vm->gt;
>
> GEM_BUG_ON(i915_vma_is_active(vma));
>
> @@ -1651,7 +1652,9 @@ static void release_references(struct i915_vma *vma, bool vm_ddestroy)
>
> spin_unlock(&obj->vma.lock);
>
> + spin_lock_irq(&gt->closed_lock);
> __i915_vma_remove_closed(vma);
> + spin_unlock_irq(&gt->closed_lock);
>
> if (vm_ddestroy)
> i915_vm_resv_put(vma->vm);
> --
> 2.35.1
>

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