From owner-freebsd-hackers  Mon Jul 23  9: 8: 6 2001
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Date: Mon, 23 Jul 2001 12:07:47 -0400 (EDT)
From: Zhihui Zhang <zzhang@cs.binghamton.edu>
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To: msmith@freebsd.org, "Eugene L. Vorokov" <vel@bugz.infotecs.ru>
Cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: using syscalls in a module (stack problem ?)
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Just out of curiosity, Linux's kernel stack is one page. Where in the
kernel source code that says that we can have two pages instead of one
page kernel stack?

-Zhihui


On Mon, 23 Jul 2001, Eugene L. Vorokov wrote:

> > > I call this function with (curproc, PATH_MAX+1), and everything is fine
> > > when I have just a few local variables defined in the caller (it all
> > > works on MOD_LOAD only). However, if I have 2 buffers, 4096 bytes each,
> > > as local variables and then try to allocate userspace memory the same
> > > way, kernel crashes - sometimes inside mmap(), sometimes a bit later.
> > > 
> > > Why could this happen ? Is it related to possible stack overflow ?
> > 
> > Yes.  The kernel stack is only two pages; you absolutely must not use 
> > large local variables in the kernel.
> 
> I see. But I still can define them using "static", right ?
> 
> Regards,
> Eugene
> 
> 
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