Re: [Patch] x86_64: TASK_SIZE fixes for compatibility mode processes

["Siddha, Suresh B" <suresh.b.siddha@intel.com>]

On Thu, Jun 02, 2005 at 01:50:13PM -0700, Andrew Morton wrote:
> "Siddha, Suresh B" <suresh.b.siddha@intel.com> wrote:
> >
> > +#define TASK_SIZE_OF(child) 	((test_tsk_thread_flag(child, TIF_IA32)) ? IA32_PAGE_OFFSET : TASK_SIZE64)
> 
> The task size is an attribute of the task's mm_struct, not of the task.

ia64, ppc64 and s390 seems be getting this info from thread_info or 
thread_struct in the task struct.

> The place where this tends to come unstuck is when a 32-bit task holds a
> reference on a 64-bit tasks's task_struct via a read of a /proc file.  If
> the 64-bit task exits then it is the 32-bit task who does the final freeing
> of the 64-bit tasks's task_struct and mm_struct.  (and all vice-versa, of
> course).  Will your patch handle this race scenario correctly?

In recent kernels, instead of TASK_SIZE, "-1" is getting passed to unmap_vmas()
from exit_mmap. Same case with ceiling (set to "0") for free_pgtables().
It shouldn't be a problem with this, right?

thanks,
suresh