Re: [PATCH] fs: fcntl_setlease defies lease_init assumptions

["Pekka Enberg" <penberg@cs.helsinki.fi>]

On 5/8/06, Linus Torvalds <torvalds@osdl.org> wrote:
> > Ok, I was actually really surprised that we'd ever allow a non-slab page
> > to be free'd as a slab or kmalloc allocation, without screaming very
> > loudly indeed. That implies a lack of some pretty fundamental sanity
> > checking by default in the slab layer (I suspect slab debugging turns it
> > on, but even without it, that's just nasty).
> >
> > Can you see if this trivial patch at least causes a honking huge
> > "kernel BUG" message to be triggered quickly?

On 5/8/06, Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> page_get_cache and page_get_slab are too late. You would need to do
> the check in __cache_free; otherwise the stack pointer goes to per-CPU
> caches and can be given back by kmalloc(). Adding PageSlab debugging
> to __cache_free is probably too much of a performance hit, though.

Btw, CONFIG_DEBUG_SLAB should catch this case, see kfree_debugcheck()
for details.

                                                  Pekka