Re: frequent slab corruption (since a long time)

From: Dave Jones
Date: Thu Aug 03 2006 - 13:55:31 EST

On Thu, Aug 03, 2006 at 06:40:42PM +0100, Alan Cox wrote:
> Ar Mer, 2006-08-02 am 15:49 -0700, ysgrifennodd David Miller:
> > > None of the code manipulating tty->count seems to be under
> > > the tty_mutex. Should it be ?
> > > Or is this protected through some other means?
> >
> > It is in the primary code paths at least, all callers of init_dev()
> > (which increments tty->count) grab the mutex and also release_dev()
> > grabs the mutex around tty->count manipulations.
> I've been auditing tty code and its joyously bad but only in harmless
> places so far except for one.
> init_dev (and caller) relies on tty_mutex to ensure that the
> driver->ttys list is protected from things going away.
> release_mem() removes stuff from the said list and frees memory. It is
> not always called under tty_mutex and that appears very dubious to me at
> the moment although tty->closing and the BKL *might* be sufficient.

Against my better judgment I was poring over that code until the wee
hours last night, and one thing crossed my mind re: the assumptions made
about the BKL in that subsystem. Now that the BKL is preemtible, do
any of those assumptions break ?


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