On Mon, Mar 05, 2012 at 05:42:56PM +0900, Namhyung Kim wrote: > 2012-03-04 7:34 PM, Minchan Kim wrote: > >Hi Namhyung, > > > > Hi Minchan, > glad to see you here again :) Thanks! > > > >On Wed, Feb 29, 2012 at 05:54:34PM +0900, Namhyung Kim wrote: > >>Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would > >>call free_pages() incorrectly on a object in a tail page, she will get > >>i confused with the undefined result. Setting the flag would help her by > >>emitting a warning on bad_page() in such a case. > >> > >>Reported-by: Sangseok Lee <sangseok.lee@xxxxxxx> > >>Signed-off-by: Namhyung Kim <namhyung.kim@xxxxxxx> > > > >I read this thread and I feel the we don't reach right point. > >I think it's not a compound page problem. > >We can face above problem where we allocates big order page without __GFP_COMP > >and free middle page of it. > > > >Fortunately, We can catch such a problem by put_page_testzero in __free_pages > >if you enable CONFIG_DEBUG_VM. > > > >Did you tried that with CONFIG_DEBUG_VM? > > > > To be honest, I don't have a real test environment which brings this > issue in the first place. On my simple test environment, enabling > CONFIG_DEBUG_VM emits a bug when I tried to free middle of the slab > pages. Thanks for pointing it out. > > However I guess there was a chance to bypass that test anyhow since > it did reach to __free_pages_ok(). If the page count was 0 already, > free_pages() will prevent it from getting to the function even > though CONFIG_DEBUG_VM was disabled. But I don't think it's a kernel > bug - it seems entirely our fault :( I'll recheck and talk about it > with my colleagues. Let me ask a question. Could you see bad page message by PG_slab with SLUB after you apply your patch? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>