On 27 April 2012 20:36, David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Fri, 27 Apr 2012, Minchan Kim wrote: > >> Now there are several places to use __vmalloc with GFP_ATOMIC, >> GFP_NOIO, GFP_NOFS but unfortunately __vmalloc calls map_vm_area >> which calls alloc_pages with GFP_KERNEL to allocate page tables. >> It means it's possible to happen deadlock. >> I don't know why it doesn't have reported until now. >> >> Firstly, I tried passing gfp_t to lower functions to support __vmalloc >> with such flags but other mm guys don't want and decided that >> all of caller should be fixed. >> >> http://marc.info/?l=linux-kernel&m=133517143616544&w=2 >> >> To begin with, let's listen other's opinion whether they can fix it >> by other approach without calling __vmalloc with such flags. >> >> So this patch adds warning to detect and to be fixed hopely. >> I Cced related maintainers. >> If I miss someone, please Cced them. >> >> side-note: >> I added WARN_ON instead of WARN_ONCE to detect all of callers >> and each WARN_ON for each flag to detect to use any flag easily. >> After we fix all of caller or reduce such caller, we can merge >> a warning with WARN_ONCE. >> > > I disagree with this approach since it's going to violently spam an > innocent kernel user's log with no ratelimiting and for a situation that > actually may not be problematic. With WARN_ON_ONCE, it should be good. > > Passing any of these bits (the difference between GFP_KERNEL and > GFP_ATOMIC) only means anything when we're going to do reclaim. And I'm > suspecting we would have seen problems with this already since > pte_alloc_kernel() does __GFP_REPEAT on most architectures meaning that it > will loop infinitely in the page allocator until at least one page is > freed (since its an order-0 allocation) which would hardly ever happen if > __GFP_FS or __GFP_IO actually meant something in this context. > > In other words, we would already have seen these deadlocks and it would > have been diagnosed as a vmalloc(GFP_ATOMIC) problem. Where are those bug > reports? That's not sound logic to disprove a bug. I think simply most callers are permissive and don't mask out flags. But for example a filesystem holding an fs lock and then doing vmalloc(GFP_NOFS) can certainly deadlock. -- 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