From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx161.postini.com [74.125.245.161]) by kanga.kvack.org (Postfix) with SMTP id 271506B0081 for ; Wed, 2 May 2012 15:46:13 -0400 (EDT) Date: Wed, 2 May 2012 12:46:10 -0700 From: Andrew Morton Subject: Re: [PATCH] vmalloc: add warning in __vmalloc Message-Id: <20120502124610.175e099c.akpm@linux-foundation.org> In-Reply-To: <1335932890-25294-1-git-send-email-minchan@kernel.org> References: <1335932890-25294-1-git-send-email-minchan@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kosaki.motohiro@gmail.com, rientjes@google.com, Neil Brown , Artem Bityutskiy , David Woodhouse , Theodore Ts'o , Adrian Hunter , Steven Whitehouse , "David S. Miller" , James Morris , Alexander Viro , Sage Weil On Wed, 2 May 2012 13:28:09 +0900 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 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@kvack.org. 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: email@kvack.org