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

[Mostafa Saleh]

On Mon, Sep 28, 2026 at 01:37:37PM -0700, Randy Dunlap wrote:
> 
> 
> 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 at 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.
> ?
> 

I will fix it in v2.

Thanks,
Mostafa

> > +
> >  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
>