linux-kernel - Re: "mm: use early_pfn_to_nid in page_ext

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170630154224.GA9714@dhcp22.suse.cz>
Date:   Fri, 30 Jun 2017 17:42:24 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.shi@...aro.org>
Cc:     Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: "mm: use early_pfn_to_nid in page_ext_init" broken on some
 configurations?

On Fri 30-06-17 16:18:47, Michal Hocko wrote:
> fe53ca54270a ("mm: use early_pfn_to_nid in page_ext_init") seem
> to silently depend on CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID resp.
> CONFIG_HAVE_MEMBLOCK_NODE_MAP. early_pfn_to_nid is returning zero with
> !defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) && !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
> I am not sure how widely is this used but such a code is tricky. I see
> how catching early allocations during defered initialization might be
> useful but a subtly broken code sounds like a problem to me.  So is
> fe53ca54270a worth this or we should revert it?

I've dug little bit further. It seems that only s390 and ia64 select
HAVE_ARCH_EARLY_PFN_TO_NID. Much more architectures enabled
HAVE_MEMBLOCK_NODE_MAP though but still
alpha, arc, arm, avr32, blackfin, c6x, cris, frv, h8300, hexagon,
Kconfig, m32r, m68k, mn10300, nios2, openrisc, parisc, tile, um,
unicore32, xtensa do not. I can only see alpha having NUMA and even that
is marked BROKEN. So it seems that this is not a real problem after all.

Still subtle, so I guess we want to have the following. What do you
think?

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 16532fa0bb64..894697c1e6f5 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1055,6 +1055,7 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist,
 	!defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
 static inline unsigned long early_pfn_to_nid(unsigned long pfn)
 {
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_NUMA));
 	return 0;
 }
 #endif
-- 
Michal Hocko
SUSE Labs