[PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed

[PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed

[Karol Herbst]

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

Re: [PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed

[Karol Herbst]

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
>

Re: [Intel-gfx] [PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed

[Tvrtko Ursulin]

On 20/04/2022 10:57, Karol Herbst 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

Fix looks correct to me. In which case it seems breakage was introduced 
with:

Fixes: 155ab8836caa ("drm/i915: Move object close under its own lock")
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: <stable@vger.kernel.org> # v5.3+

AFAICT at least. I will add these tags and pull it in unless someone 
shouts a correction.

Regards,

Tvrtko

> 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);

Re: [Intel-gfx] [PATCH v2] drm/i915: Fix race in __i915_vma_remove_closed

[Tvrtko Ursulin]

On 20/04/2022 10:57, Karol Herbst 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>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

> ---
>   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);