From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757297Ab2ECLIy (ORCPT ); Thu, 3 May 2012 07:08:54 -0400 Received: from mga03.intel.com ([143.182.124.21]:32816 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752846Ab2ECLIw (ORCPT ); Thu, 3 May 2012 07:08:52 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="asc'?scan'208";a="138393419" Message-ID: <1336043475.13013.47.camel@sauron.fi.intel.com> Subject: Re: [PATCH] vmalloc: add warning in __vmalloc From: Artem Bityutskiy Reply-To: dedekind1@gmail.com To: Andrew Morton Cc: Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kosaki.motohiro@gmail.com, rientjes@google.com, Neil Brown , David Woodhouse , "Theodore Ts'o" , Adrian Hunter , Steven Whitehouse , "David S. Miller" , James Morris , Alexander Viro , Sage Weil Date: Thu, 03 May 2012 14:11:15 +0300 In-Reply-To: <20120502124610.175e099c.akpm@linux-foundation.org> References: <1335932890-25294-1-git-send-email-minchan@kernel.org> <20120502124610.175e099c.akpm@linux-foundation.org> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-57Lh1wuEjZihfs+vd2pa" X-Mailer: Evolution 3.2.3 (3.2.3-3.fc16) Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-57Lh1wuEjZihfs+vd2pa Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2012-05-02 at 12:46 -0700, Andrew Morton wrote: > On Wed, 2 May 2012 13:28:09 +0900 > Minchan Kim wrote: >=20 > > 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. > >=20 > > 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. > >=20 > > http://marc.info/?l=3Dlinux-kernel&m=3D133517143616544&w=3D2 > >=20 > > To begin with, let's listen other's opinion whether they can fix it > > by other approach without calling __vmalloc with such flags. > >=20 > > 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_a= rea_node. > > And __vmalloc_area_node is current static function and is called by onl= y > > __vmalloc_node_range. So warning in __vmalloc_node_range would cover al= l > > vmalloc functions which have gfp_t argument. > > > > I Cced related maintainers. > > If I miss someone, please Cced them. > >=20 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1648,6 +1648,10 @@ void *__vmalloc_node_range(unsigned long size, u= nsigned long align, > > void *addr; > > unsigned long real_size =3D size; > > =20 > > + WARN_ON_ONCE(!(gfp_mask & __GFP_WAIT) || > > + !(gfp_mask & __GFP_IO) || > > + !(gfp_mask & __GFP_FS)); > > + > > size =3D PAGE_ALIGN(size); > > if (!size || (size >> PAGE_SHIFT) > totalram_pages) > > goto fail; >=20 > 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. >=20 > This isn't very efficient :( >=20 > 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. =20 >=20 > 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. --=20 Best Regards, Artem Bityutskiy --=-57Lh1wuEjZihfs+vd2pa Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAABAgAGBQJPomfTAAoJECmIfjd9wqK0Le0P/jVKUGL5CYTbVVuaczEr0YHG 3u1H1H5PdbSh+nZh1k+B4954w5tS96bPRrJi2HsFGTSdAvWudF0w5jOaXZqxE9y9 JRIqsYO1n4yJcYM6vNFOTOxk0gUCap4hR+AvqBGEB8C/fiC3f5E/FxISwSrzLBFx xMaScsYuaJJv0IzOD+MuPEDW2YuX3dyiKssqh8yWIcPNtS/o8LQ/im06HZugYvXo cuslXW3/vtcV7npEvyXNxRioKlsouWfuEh2ukrIvHRN7hGgAkUeW87ht2Z10065U oK+kWKd8PjrT7j0tzjnbGWZNkgUnIzo+4p91RzszfdVo/pZRQRogNAT4U6zRwbMZ MoW9prWmwT57iI4MIu9eCvqMug+nQesCvMlok7Bh8bvESxl6+CzTGGu0VwjKkUty xgPH3XRDGjrPPGwOUDL4Rv9ugCh8IVQE4punSIjGxwVrjtEDpLGObF7bj2Zzl46Q 7ye17JDT3p4HwtNgcDvNCUlyZ7xT2hReSQ8+GOMGuH94Wz9okMAg/eF2UHGsT1+d pbcy2a2YbikOooG1hVMcKf3YjJHeMwVNH/Eag8zpcKg5+Hl7Gf/BxrbzetubAow2 /i01lJ7nYieCXTp+AzJiRsaBIiQ7YXhcY6pK4NCu5EeQJfl9ugxyoUBGr7h/6YlG h5DV5VzMJrgsGpxoKonm =U6kO -----END PGP SIGNATURE----- --=-57Lh1wuEjZihfs+vd2pa--