linux-kernel - vmemmap_verify() BUGs during memory hotplug (4.2-rc1 regression)

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 for Android: free password hash cracker in your pocket

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

Message-ID: <55B64F1D.8090807@citrix.com>
Date:	Mon, 27 Jul 2015 16:32:45 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: vmemmap_verify() BUGs during memory hotplug (4.2-rc1 regression)

Mel,

As of commit 8a942fdea560d4ac0e9d9fabcd5201ad20e0c382 (mm: meminit: make
__early_pfn_to_nid SMP-safe and introduce meminit_pfn_in_nid)
vmemmap_verify() will BUG_ON() during memory hotplug because of its use
of early_pfn_to_nid().  Previously, it would have reported bogus (or
failed to report valid) warnings.

I believe this does not affect memory hotplug on most x86 systems
because vmemmap_populate() would normally call
vmemmap_populate_hugepages() which avoids calling vmemmap_verify() in
the common case (no existing mappings covering the new area).

I'm triggering the early_pfn_to_nid() BUG_ON() with the Xen balloon
driver in a PV guest which will always call vmemmap_populate_basepages()
(since Xen PV guests lack superpage support).

Not really sure what the best way to resolve this is.  Presumably
vmmemmap_verify() needs to switch to using pfn_to_nid() after the
initial initialization but there doesn't appear to be anything suitable
to distinguish between the early and hotplug cases.

David

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/