Re: kernel stack

[suthambhara nagaraj]

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@xxxxxxxxxx> 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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> --
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>  *Neil Horman
>  *Software Engineer
>  *Red Hat, Inc.
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