On Wed, 2 May 2012 13:28:09 +0900 Minchan Kim <minchan@xxxxxxxxxx> 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 in __vmalloc_node_range to detect it and > to be fixed hopely. __vmalloc_node_range isn't random chocie because > all caller which has gfp_mask of map_vm_area use it through __vmalloc_area_node. > And __vmalloc_area_node is current static function and is called by only > __vmalloc_node_range. So warning in __vmalloc_node_range would cover all > vmalloc functions which have gfp_t argument. > > I Cced related maintainers. > If I miss someone, please Cced them. > > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1648,6 +1648,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, > void *addr; > unsigned long real_size = size; > > + WARN_ON_ONCE(!(gfp_mask & __GFP_WAIT) || > + !(gfp_mask & __GFP_IO) || > + !(gfp_mask & __GFP_FS)); > + > size = PAGE_ALIGN(size); > if (!size || (size >> PAGE_SHIFT) > totalram_pages) > goto fail; Well. What are we actually doing here? Causing the kernel to spew a warning due to known-buggy callsites, so that users will report the warnings, eventually goading maintainers into fixing their stuff. This isn't very efficient :( It would be better to fix that stuff first, then add the warning to prevent reoccurrences. Yes, maintainers are very naughty and probably do need cattle prods^W^W warnings to motivate them to fix stuff, but we should first make an effort to get these things fixed without irritating and alarming our users. Where are these offending callsites? -- 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>