Re: export of sys_call_table

["Brian F. G. Bidulock" <bidulock@openss7.org>]

Andi,

On Fri, 04 Oct 2002, Andi Kleen wrote:

> > Well, for LiS, a process does not sleep on read_lock whenever write_lock
> > might be called.  This is because only invalid getpmsg/putpmsg calls
> 
> See the "userptr" argument. The only way to access it is a 
> copy_from/to_user, and that sleeps.

The invalid argument is the fd, so no copy_from/to_user can occur
while another processor spins on the write_lock().

> 
> > (wrong file descriptor) can be made during module loading and unloading.
> > No valid file descriptors exist for getpmsg/putpmsg when the module is
> > unloading (proper use of MOD_INC/DEC_USE_COUNT).  I don't see that it
> > matters that a process sleeps holding a read_lock() when it is a given
> > that the write_lock() will never be attempted while the holder of the
> > read_lock() is sleeping.
> 
> ... Just you cannot guarantee that, except for never taking the write_lock,
> which would make the whole exercise quite pointless.

Yes, it is guaranteed by module use counts.

--brian

-- 
Brian F. G. Bidulock    ¦ The reasonable man adapts himself to the ¦
bidulock@openss7.org    ¦ world; the unreasonable one persists in  ¦
http://www.openss7.org/ ¦ trying  to adapt the  world  to himself. ¦
                        ¦ Therefore  all  progress  depends on the ¦
                        ¦ unreasonable man. -- George Bernard Shaw ¦