On Mon, 25 Oct 2010 15:10:25 +0200 Michal Hocko <mhocko@xxxxxxx> wrote: > On Mon 25-10-10 15:49:33, Wu Fengguang wrote: > > On Mon, Oct 25, 2010 at 02:37:26PM +0800, KAMEZAWA Hiroyuki wrote: > > > I wonder this should be for stable tree...but want to hear opinions before. > > > == > > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > > > > > page_order() is called by memory hotplug's user interface to check > > > the section is removable or not. (is_mem_section_removable()) > > > > > > It calls page_order() withoug holding zone->lock. > > > So, even if the caller does > > > > > > if (PageBuddy(page)) > > > ret = page_order(page) ... > > > The caller may hit BUG_ON(). > > > > > > For fixing this, there are 2 choices. > > > 1. add zone->lock. > > > 2. remove BUG_ON(). > > > > One more alternative might be to introduce a private > > maybe_page_order() for is_mem_section_removable(). Not a big deal. > > I guess this is not necessary as all page_order callers check PageBuddy > anyway AFAICS. And hold zone->lock, one hopes. > > > > > is_mem_section_removable() is used for some "advice" and doesn't need > > > to be 100% accurate. This is_removable() can be called via user program.. > > > We don't want to take this important lock for long by user's request. > > > So, this patch removes BUG_ON(). > > > > Acked-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > > Yes, the change looks good. It removes a valid assertion because one of the callers is doing something exceptional. That exceptional caller should implement the exceptional code, rather than weakening useful code for other callers! But I'll grab the patch anyway, since BUG_ON in an inlined function is a pretty bad idea from a bloat POV. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>