On Wed, 2012-05-02 at 12:46 -0700, Andrew Morton wrote: > 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? OK, I checked my part - both UBI and UBIFS call __vmalloc() with GFP_NOFS in several places of the _debugging_ code, and this is why we do not see any issues - the debugging code is used very rarely for validating purposes. All the places look fixable, I'll fix them a bit later. WARN_ON_ONCE() looks like a good first step. An I think it is better if maintainers fix their areas rather than if someone who does not know how the subsystem works starts trying to do that. -- Best Regards, Artem Bityutskiy
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