Re: [Oops] i386 mm/slab.c (cache_flusharray)

[Nathan Scott <nathans@sgi.com>]

On Thu, Dec 04, 2003 at 11:09:29AM -0800, Linus Torvalds wrote:
> 
> 
> On Thu, 4 Dec 2003, Linus Torvalds wrote:
> > > ---
> > > kernel BUG at include/linux/mm.h:267!
> >
> > YEAH! That's "put_page_testzero()", and either the BUG_ON() or the
> > atomic_dec_and_test() noticing bad things.
> 
> Oh, damn. Looking closer, it appears that it's actually XFS being a bit
> too intimate with slab knowledge: the code does
> 
>                         if (pb->pb_pages) {
>                                 /* release the pages in the address list */
>                                 if (pb->pb_pages[0] &&
>                                     PageSlab(pb->pb_pages[0])) {
>                                         /*
>                                          * This came from the slab
>                                          * allocator free it as such
>                                          */
>                                         kfree(pb->pb_addr);
>                                 } else {
>                                         _pagebuf_freepages(pb);
>                                 }
> 
> and that code gets really confused by the fact that I'm bypassing the slab
> logic (and thus the PageSlab flag never gets set).
> 
> So the oops it found was apparently triggered by the debugging changes,
> not necessarily by a real bug.
> 
> Ugh, that XFS code is _broken_. Instead of keeping track of how it got the
> memory, it totally forgets where the memory came from, and then it later
> asks "oh, btw, how the hell did I allocate this?".

Yeah, thats pretty silly stuff - and should be fairly easy to
fix by using a pagebuf flag to differentiate the two.  Will do.

thanks.

-- 
Nathan