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  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]
Date:   Thu, 30 Aug 2018 19:37:34 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     David Hildenbrand <david@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Rashmica Gupta <rashmica.g@...il.com>,
        Michael Neuling <mikey@...ling.org>,
        Balbir Singh <bsingharora@...il.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Oscar Salvador <osalvador@...e.de>,
        YASUAKI ISHIMATSU <yasu.isimatu@...il.com>,
        Mathieu Malaterre <malat@...ian.org>
Subject: Re: [PATCH RFCv2 3/6] mm/memory_hotplug: fix online/offline_pages
 called w.o. mem_hotplug_lock

On 8/21/18 6:44 AM, David Hildenbrand wrote:
> There seem to be some problems as result of 30467e0b3be ("mm, hotplug:
> fix concurrent memory hot-add deadlock"), which tried to fix a possible
> lock inversion reported and discussed in [1] due to the two locks
> 	a) device_lock()
> 	b) mem_hotplug_lock
> 
> While add_memory() first takes b), followed by a) during
> bus_probe_device(), onlining of memory from user space first took b),
> followed by a), exposing a possible deadlock.
> 
> In [1], and it was decided to not make use of device_hotplug_lock, but
> rather to enforce a locking order.
> 
> The problems I spotted related to this:
> 
> 1. Memory block device attributes: While .state first calls
>    mem_hotplug_begin() and the calls device_online() - which takes
>    device_lock() - .online does no longer call mem_hotplug_begin(), so
>    effectively calls online_pages() without mem_hotplug_lock.
> 
> 2. device_online() should be called under device_hotplug_lock, however
>    onlining memory during add_memory() does not take care of that.
> 
> In addition, I think there is also something wrong about the locking in
> 
> 3. arch/powerpc/platforms/powernv/memtrace.c calls offline_pages()
>    without locks. This was introduced after 30467e0b3be. And skimming over
>    the code, I assume it could need some more care in regards to locking
>    (e.g. device_online() called without device_hotplug_lock - but I'll
>    not touch that for now).
> 
> Now that we hold the device_hotplug_lock when
> - adding memory (e.g. via add_memory()/add_memory_resource())
> - removing memory (e.g. via remove_memory())
> - device_online()/device_offline()
> 
> We can move mem_hotplug_lock usage back into
> online_pages()/offline_pages().
> 
> Why is mem_hotplug_lock still needed? Essentially to make
> get_online_mems()/put_online_mems() be very fast (relying on
> device_hotplug_lock would be very slow), and to serialize against
> addition of memory that does not create memory block devices (hmm).
> 
> [1] http://driverdev.linuxdriverproject.org/pipermail/ driverdev-devel/
>     2015-February/065324.html
> 
> This patch is partly based on a patch by Vitaly Kuznetsov.

Reviewed-by: Pavel Tatashin <pavel.tatashin@...rosoft.com>

Powered by blists - more mailing lists