[PATCH] arm64/gcs: Don't call gcs_free() when releasing task_struct

[PATCH] arm64/gcs: Don't call gcs_free() when releasing task_struct

[Mark Brown]

Currently we call gcs_free() when releasing task_struct but this is
redundant, it attempts to deallocate any kernel managed userspace GCS
which should no longer be relevant and resets values in the struct we're
in the process of freeing.

By the time arch_release_task_struct() is called the mm will have been
disassociated from the task so the check for a mm in gcs_free() will
always be false, for threads that are exiting leaving the mm active
deactivate_mm() will have been called previously and freed any kernel
managed GCS.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/kernel/process.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 5954cec19660..5dcfab9ce012 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -341,7 +341,6 @@ void flush_thread(void)
 void arch_release_task_struct(struct task_struct *tsk)
 {
 	fpsimd_release_task(tsk);
-	gcs_free(tsk);
 }
 
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)

---
base-commit: 86731a2a651e58953fc949573895f2fa6d456841
change-id: 20250610-arm64-gcs-release-task-307db60fa1b4

Best regards,
--  
Mark Brown <broonie@kernel.org>

Re: [PATCH] arm64/gcs: Don't call gcs_free() when releasing task_struct

[Will Deacon]

On Wed, Jun 25, 2025 at 07:56:34PM +0100, Mark Brown wrote:
> Currently we call gcs_free() when releasing task_struct but this is
> redundant, it attempts to deallocate any kernel managed userspace GCS
> which should no longer be relevant and resets values in the struct we're
> in the process of freeing.
> 
> By the time arch_release_task_struct() is called the mm will have been
> disassociated from the task so the check for a mm in gcs_free() will
> always be false, for threads that are exiting leaving the mm active
> deactivate_mm() will have been called previously and freed any kernel
> managed GCS.
> 
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
>  arch/arm64/kernel/process.c | 1 -
>  1 file changed, 1 deletion(-)

Thanks, but please can you also update/remove the stale comment in
gcs_free() which refers to exit_thread() for some reason?

Cheers,

Will