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Subject: Re: [PATCH v1] xen/balloon: Set pages PageOffline() in
 balloon_add_region()
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, xen-devel@lists.xenproject.org,
        =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= 
        <marmarek@invisiblethingslab.com>, stable@vger.kernel.org,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>
References: <20190927154628.8480-1-david@redhat.com>
 <4d6a1f9b-15ff-6594-44e0-bc262e9347f7@oracle.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <f591f279-62c9-3d3d-39ad-090c2ad73c23@redhat.com>
Date:   Sat, 28 Sep 2019 10:46:18 +0200
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On 27.09.19 20:08, Boris Ostrovsky wrote:
> On 9/27/19 11:46 AM, David Hildenbrand wrote:
>> We are missing a __SetPageOffline(), which is why we can get
>> !PageOffline() pages onto the balloon list, where
>> alloc_xenballooned_pages() will complain:
>>
>> page:ffffea0003e7ffc0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
>> flags: 0xffffe00001000(reserved)
>> raw: 000ffffe00001000 dead000000000100 dead000000000200 0000000000000000
>> raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
>> page dumped because: VM_BUG_ON_PAGE(!PageOffline(page))
>> ------------[ cut here ]------------
>> kernel BUG at include/linux/page-flags.h:744!
>> invalid opcode: 0000 [#1] SMP NOPTI
>>
>> Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
>> Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
>> Fixes: 77c4adf6a6df ("xen/balloon: mark inflated pages PG_offline")
>> Cc: stable@vger.kernel.org # v5.1+
>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> Cc: Juergen Gross <jgross@suse.com>
>> Cc: Stefano Stabellini <sstabellini@kernel.org>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  drivers/xen/balloon.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index 05b1f7e948ef..29f6256363db 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -687,6 +687,7 @@ static void __init balloon_add_region(unsigned long start_pfn,
>>  		/* totalram_pages and totalhigh_pages do not
>>  		   include the boot-time balloon extension, so
>>  		   don't subtract from it. */
>> +		__SetPageOffline(page);
>>  		__balloon_append(page);
> 
> 
> Given that when a page is appended to balloon list need to be marked
> offline and, conversely, when a page is retrieved the bit should be
> cleared I wonder whether it's better to move Set/ClearPageOffline to
> balloon_append/retrieve().

Yes, we can do that as an addon patch (and also get rid of either
__balloon_append() or balloon_append() if I remember correctly).

-- 

Thanks,

David / dhildenb