mm: task_stack: Stack handling cleanups

[PATCH 1/2] fork: check charging success before zeroing stack

Posted by Linus Walleij 1 month ago

From: Pasha Tatashin <pasha.tatashin@soleen.com>

No need to do zero cached stack if memcg charge fails, so move the
charging attempt before the memset operation.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/20240311164638.2015063-6-pasha.tatashin@soleen.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 kernel/fork.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index af673856499dcaa35e135a9e8042ef28d5c5370d..2a5b7a5fa09b1f3a42473cf44a1316ec8b3b31d0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -290,6 +290,11 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 		if (!vm_area)
 			continue;
 
+		if (memcg_charge_kernel_stack(vm_area)) {
+			vfree(vm_area->addr);
+			return -ENOMEM;
+		}
+
 		/* Reset stack metadata. */
 		kasan_unpoison_range(vm_area->addr, THREAD_SIZE);
 
@@ -298,11 +303,6 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 		/* Clear stale pointers from reused stack. */
 		memset(stack, 0, THREAD_SIZE);
 
-		if (memcg_charge_kernel_stack(vm_area)) {
-			vfree(vm_area->addr);
-			return -ENOMEM;
-		}
-
 		tsk->stack_vm_area = vm_area;
 		tsk->stack = stack;
 		return 0;

-- 
2.50.1

Re: [PATCH 1/2] fork: check charging success before zeroing stack

Posted by Lorenzo Stoakes 1 month ago

On Fri, Aug 29, 2025 at 01:44:40PM +0200, Linus Walleij wrote:
> From: Pasha Tatashin <pasha.tatashin@soleen.com>
>
> No need to do zero cached stack if memcg charge fails, so move the
> charging attempt before the memset operation.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Link: https://lore.kernel.org/20240311164638.2015063-6-pasha.tatashin@soleen.com
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  kernel/fork.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index af673856499dcaa35e135a9e8042ef28d5c5370d..2a5b7a5fa09b1f3a42473cf44a1316ec8b3b31d0 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -290,6 +290,11 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>  		if (!vm_area)
>  			continue;
>
> +		if (memcg_charge_kernel_stack(vm_area)) {
> +			vfree(vm_area->addr);
> +			return -ENOMEM;
> +		}
> +
>  		/* Reset stack metadata. */
>  		kasan_unpoison_range(vm_area->addr, THREAD_SIZE);
>
> @@ -298,11 +303,6 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>  		/* Clear stale pointers from reused stack. */
>  		memset(stack, 0, THREAD_SIZE);
>
> -		if (memcg_charge_kernel_stack(vm_area)) {
> -			vfree(vm_area->addr);
> -			return -ENOMEM;
> -		}
> -
>  		tsk->stack_vm_area = vm_area;
>  		tsk->stack = stack;
>  		return 0;
>
> --
> 2.50.1
>

Re: [PATCH 1/2] fork: check charging success before zeroing stack

Posted by Liam R. Howlett 1 month ago

* Linus Walleij <linus.walleij@linaro.org> [250829 07:44]:
> From: Pasha Tatashin <pasha.tatashin@soleen.com>
> 
> No need to do zero cached stack if memcg charge fails, so move the
> charging attempt before the memset operation.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> Link: https://lore.kernel.org/20240311164638.2015063-6-pasha.tatashin@soleen.com
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>


Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> ---
>  kernel/fork.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index af673856499dcaa35e135a9e8042ef28d5c5370d..2a5b7a5fa09b1f3a42473cf44a1316ec8b3b31d0 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -290,6 +290,11 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>  		if (!vm_area)
>  			continue;
>  
> +		if (memcg_charge_kernel_stack(vm_area)) {
> +			vfree(vm_area->addr);
> +			return -ENOMEM;
> +		}
> +
>  		/* Reset stack metadata. */
>  		kasan_unpoison_range(vm_area->addr, THREAD_SIZE);
>  
> @@ -298,11 +303,6 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
>  		/* Clear stale pointers from reused stack. */
>  		memset(stack, 0, THREAD_SIZE);
>  
> -		if (memcg_charge_kernel_stack(vm_area)) {
> -			vfree(vm_area->addr);
> -			return -ENOMEM;
> -		}
> -
>  		tsk->stack_vm_area = vm_area;
>  		tsk->stack = stack;
>  		return 0;
> 
> -- 
> 2.50.1
>