[PATCH] rust: DamFence: Remove warning about unsignaled drop

[PATCH] rust: DamFence: Remove warning about unsignaled drop

[Philipp Stanner]

DriverFence::drop() contains a pr_warn!() for when the fence drops
unsignaled. This warning gets into the way of canonical teardown in
Rust: when you drop a lock, it unlocks itself, when you drop a KBox, it
frees itself etc. Congruently, users should be able to tear down fences
they don't care about anymore with ECANCELED, which is already the
default error code.

Remove the warning.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
---
 rust/kernel/dma_buf/dma_fence.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/rust/kernel/dma_buf/dma_fence.rs b/rust/kernel/dma_buf/dma_fence.rs
index a1d851656562..2c8001cb9a59 100644
--- a/rust/kernel/dma_buf/dma_fence.rs
+++ b/rust/kernel/dma_buf/dma_fence.rs
@@ -942,7 +942,6 @@ fn drop(&mut self) {
         // SAFETY: `guard` is valid until the `call_rcu()` below.
         let signaled: bool = unsafe { bindings::dma_fence_test_signaled_flag(guard.as_raw()) };
         if !signaled {
-            pr_err!("DriverFence drops unsignaled. Danger of memory corruption!\n");
             // SAFETY: `guard` is valid until the `call_rcu()` below. The fence
             // must not have been signaled yet, which we check directly above.
             unsafe { bindings::dma_fence_set_error(guard.as_raw(), ECANCELED.to_errno()) };
-- 
2.56.0

Re: [PATCH] rust: DamFence: Remove warning about unsignaled drop

[Christian König]

On 11/12/26 11:10, Philipp Stanner wrote:
> DriverFence::drop() contains a pr_warn!() for when the fence drops
> unsignaled. This warning gets into the way of canonical teardown in
> Rust: when you drop a lock, it unlocks itself, when you drop a KBox, it
> frees itself etc. Congruently, users should be able to tear down fences
> they don't care about anymore with ECANCELED, which is already the
> default error code.

Well a dma_fence should never automatically signal when the last reference drops.

Leaving it unsignaled is the most defensive path we can go. That can lead to deadlocks but it can at least not lead to memory corruption.

Regards,
Christian.

> 
> Remove the warning.
> 
> Suggested-by: Danilo Krummrich <dakr@kernel.org>
> Signed-off-by: Philipp Stanner <phasta@kernel.org>
> ---
>  rust/kernel/dma_buf/dma_fence.rs | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/rust/kernel/dma_buf/dma_fence.rs b/rust/kernel/dma_buf/dma_fence.rs
> index a1d851656562..2c8001cb9a59 100644
> --- a/rust/kernel/dma_buf/dma_fence.rs
> +++ b/rust/kernel/dma_buf/dma_fence.rs
> @@ -942,7 +942,6 @@ fn drop(&mut self) {
>          // SAFETY: `guard` is valid until the `call_rcu()` below.
>          let signaled: bool = unsafe { bindings::dma_fence_test_signaled_flag(guard.as_raw()) };
>          if !signaled {
> -            pr_err!("DriverFence drops unsignaled. Danger of memory corruption!\n");
>              // SAFETY: `guard` is valid until the `call_rcu()` below. The fence
>              // must not have been signaled yet, which we check directly above.
>              unsafe { bindings::dma_fence_set_error(guard.as_raw(), ECANCELED.to_errno()) };