Re: [RFC PATCH 12/15] sched/task_stack: Introduce ARCH_HAS_VARIABLE_STACK_SIZE

[Randy Dunlap <rdunlap@infradead.org>]

On 9/28/26 10:41 AM, Mostafa Saleh wrote:
> When CONFIG_ARCH_HAS_VARIABLE_STACK_SIZE is enabled, the kernel stack
> may not be fully populated with the THREAD_SIZE virtual area.
> 
> Teach task_stack_size() to return the size of the vm area and not a
> fixed size.
> 
> This propagates to end_of_stack() which makes functions like
> stack_not_used() and set_task_stack_end_magic() to use the lowest
> valid stack address instead of THREAD_SIZE which would cause data
> aborts.
> 
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>  arch/Kconfig                     | 10 ++++++++++
>  include/linux/sched/task_stack.h |  5 +++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 45c657772362..d6fa2ccb0599 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -431,6 +431,16 @@ config HAVE_ASM_MODVERSIONS
>  	  <asm/asm-prototypes.h> to support the module versioning for symbols
>  	  exported from assembly code.
>  
> +config ARCH_HAS_VARIABLE_STACK_SIZE
> +	bool
> +	depends on VMAP_STACK
> +	depends on !STACK_GROWSUP
> +	depends on THREAD_INFO_IN_TASK
> +	help
> +	  An arch should select this if it supports dynamically configuring the
> +	  kernel stack size.
> +	  For example the kernel stack size can be from the command line.

	                                    can be set from the command line.
?

> +
>  config HAVE_REGS_AND_STACK_ACCESS_API
>  	bool
>  	help
> diff --git a/include/linux/sched/task_stack.h b/include/linux/sched/task_stack.h
> index 4a808f9c4631..07d73adaecd1 100644
> --- a/include/linux/sched/task_stack.h
> +++ b/include/linux/sched/task_stack.h
> @@ -10,6 +10,7 @@
>  #include <linux/magic.h>
>  #include <linux/refcount.h>
>  #include <linux/kasan.h>
> +#include <linux/vmalloc.h>
>  
>  #ifdef CONFIG_THREAD_INFO_IN_TASK
>  
> @@ -96,6 +97,10 @@ static inline unsigned long *end_of_stack(const struct task_struct *p)
>   */
>  static __always_inline unsigned long task_stack_size(const struct task_struct *task)
>  {
> +#ifdef CONFIG_ARCH_HAS_VARIABLE_STACK_SIZE
> +	if (task->stack_vm_area)
> +		return task->stack_vm_area->nr_pages * PAGE_SIZE;
> +#endif
>  	return THREAD_SIZE;
>  }
>  

-- 
~Randy