[PATCH RFCv2 3/6] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock

From: Rashmica <rashmica.g@gmail.com>
To: David Hildenbrand <david@redhat.com>, linux-mm@kvack.org
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
	Michal Hocko <mhocko@suse.com>,
	linux-doc@vger.kernel.org,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Paul Mackerras <paulus@samba.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Michael Neuling <mikey@neuling.org>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Pavel Tatashin <pasha.tatashin@oracle.com>,
	linux-acpi@vger.kernel.org, xen-devel@lists.xenproject.org,
	Len Brown <lenb@kernel.org>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Dan Williams <dan.j.williams@intel.com>,
	YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Oscar Salvador <osalvador@suse.de>,
	Juergen Gross <jgross@suse.com>,
	Math
Subject: [PATCH RFCv2 3/6] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
Date: Mon, 3 Sep 2018 10:36:24 +1000	[thread overview]
Message-ID: <70372ef5-e332-6c07-f08c-50f8808bde6d@gmail.com> (raw)
In-Reply-To: <20180821104418.12710-4-david@redhat.com>

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Hi David,

On 21/08/18 20:44, 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.

Do you mean "onlining of memory from user space first took a),
followed by b)"? 

> 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).

Can you mention that you fixed this in later patches?

The series looks good to me. Feel free to add my reviewed-by:

Reviewed-by: Rashmica Gupta <rashmica.g@gmail.com>

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