2022-04-21 05:25:33

by Karol Herbst

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

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 <[email protected]>
Cc: [email protected]
Cc: [email protected]
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
Signed-off-by: Karol Herbst <[email protected]>
---
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

2022-05-03 01:07:24

by Karol Herbst

Subject: Re: [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 <[email protected]> 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 <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
> Signed-off-by: Karol Herbst <[email protected]>
> ---
> 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
>

2022-05-03 10:07:45

by Tvrtko Ursulin

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

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 <[email protected]>
Cc: <[email protected]> # v5.3+

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

Regards,

Tvrtko

> Cc: Chris Wilson <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
> Signed-off-by: Karol Herbst <[email protected]>
> ---
> 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);

2022-05-04 22:52:11

by Tvrtko Ursulin

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

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 <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5732
> Signed-off-by: Karol Herbst <[email protected]>

Reviewed-by: Tvrtko Ursulin <[email protected]>

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);