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SubjectRe: kernel stack
Thanks Neil. I was an idiot to have overlooked  that.
Thanks once again

Regards
Suthambhara


On Tue, 12 Oct 2004 07:09:09 -0400, Neil Horman <nhorman@redhat.com> wrote:
>
>
> suthambhara nagaraj wrote:
> > Hi all,
> >
> > I have not understood how the common kernel stack in the
> > init_thread_union(2.6 ,init_task_union in case of 2.4) works for all
> > the processes which run on the same processor. The scheduling is round
> > robin and yet the things on the stack (saved during SAVE_ALL) have to
> > be maintained after a switch without them getting erased. I am
> > familiar with only the i386 arch implementation.
> >
> > Please help
> >
> There is no such thing as "the common kernel stack". Each process
> (represented by a task_struct in the kernel) has its own private data
> space to be used as a kernel stack when that process traps into the
> kernel. You can see where this per task_struct stack space is reserved
> in the definition of task_union. init_[task|thread]_union just defines
> the first task union in the system. Because of the way unions are laid
> out in memory, The kernel knows that when a process traps into kernel
> space, it just needs to round the current task pointer to the nearest 8k
> (prehaps 4k in 2.6) boundary, and thats the start of that processes
> kernel stack. Thats how the SAVE_ALL command avoids trampling registers.
>
> HTH
> Neil
> > regards,
> > Suthambhara
> > -
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> --
> /***************************************************
> *Neil Horman
> *Software Engineer
> *Red Hat, Inc.
> *nhorman@redhat.com
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> *http://pgp.mit.edu
> ***************************************************/
>
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