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 ¦
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This archive was generated by hypermail 2b29 : Mon Oct 07 2002 - 22:00:44 EST