Re: kernel stack

[suthambhara nagaraj]

Hi all,

I went through the code of do_fork.
do_fork calls copy_process which in turn calls 
dup_task_struct .Here alloc_thread_info allocates the 
kernel stack for the process

Thanks all

Regards
Suthambhara


On Wed, 13 Oct 2004 08:59:14 +0530, suthambhara nagaraj
<suthambhara@xxxxxxxxx> wrote:
> 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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> > --
> > /***************************************************
> >  *Neil Horman
> >  *Software Engineer
> >  *Red Hat, Inc.
> >  *nhorman@xxxxxxxxxx
> >  *gpg keyid: 1024D / 0x92A74FA1
> >  *http://pgp.mit.edu
> >  ***************************************************/
> >
>
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