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Subject: Re: [PATCH] mm/memory_hotplug: Drop memory device reference after
 find_memory_block()
To:     Michal Hocko <mhocko@kernel.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Wei Yang <richard.weiyang@gmail.com>, Qian Cai <cai@lca.pw>,
        Arun KS <arunks@codeaurora.org>,
        Mathieu Malaterre <malat@debian.org>
References: <20190410101455.17338-1-david@redhat.com>
 <20190411084141.GQ10383@dhcp22.suse.cz>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <0bbe632f-cb85-4a98-0c79-ded11cf39081@redhat.com>
Date:   Thu, 11 Apr 2019 11:11:05 +0200
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On 11.04.19 10:41, Michal Hocko wrote:
> On Wed 10-04-19 12:14:55, David Hildenbrand wrote:
>> While current node handling is probably terribly broken for memory block
>> devices that span several nodes (only possible when added during boot,
>> and something like that should be blocked completely), properly put the
>> device reference we obtained via find_memory_block() to get the nid.
> 
> The changelog could see some improvements I believe. (Half) stating
> broken status of multinode memblock is not really useful without a wider
> context so I would simply remove it. More to the point, it would be much
> better to actually describe the actual problem and the user visible
> effect.
> 
> "
> d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug") has started
> using find_memory_block to get a nodeid for the beginnig of the onlined
> pfn range. The commit has missed that the memblock contains a reference
> counted object and a missing put_device will leak the kobject behind
> which ADD THE USER VISIBLE EFFECT HERE.
> "

I don't think mentioning the commit a second time is really needed.

"
Right now we are using find_memory_block() to get the node id for the
pfn range to online. We are missing to drop a reference to the memory
block device. While the device still gets unregistered via
device_unregister(), resulting in no user visible problem, the device is
never released via device_release(), resulting in a memory leak. Fix
that by properly using a put_device().
"

> 
>> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Wei Yang <richard.weiyang@gmail.com>
>> Cc: Qian Cai <cai@lca.pw>
>> Cc: Arun KS <arunks@codeaurora.org>
>> Cc: Mathieu Malaterre <malat@debian.org>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Other than that
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
>> ---
>>  mm/memory_hotplug.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 5eb4a4c7c21b..328878b6799d 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -854,6 +854,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>>  	 */
>>  	mem = find_memory_block(__pfn_to_section(pfn));
>>  	nid = mem->nid;
>> +	put_device(&mem->dev);
>>  
>>  	/* associate pfn range with the zone */
>>  	zone = move_pfn_range(online_type, nid, pfn, nr_pages);
>> -- 
>> 2.20.1
> 


-- 

Thanks,

David / dhildenb