Re: [Xen-devel] [PATCH v2 5/6] powerpc/powernv: hold device_hotplug_lock when calling memtrace_offline_pages()

[David Hildenbrand <david@xxxxxxxxxx>]

On 25/09/2018 14:15, Balbir Singh wrote:
> On Tue, Sep 25, 2018 at 11:14:56AM +0200, David Hildenbrand wrote:
>> Let's perform all checking + offlining + removing under
>> device_hotplug_lock, so nobody can mess with these devices via
>> sysfs concurrently.
>>
>> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
>> Cc: Paul Mackerras <paulus@xxxxxxxxx>
>> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
>> Cc: Rashmica Gupta <rashmica.g@xxxxxxxxx>
>> Cc: Balbir Singh <bsingharora@xxxxxxxxx>
>> Cc: Michael Neuling <mikey@xxxxxxxxxxx>
>> Reviewed-by: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
>> Reviewed-by: Rashmica Gupta <rashmica.g@xxxxxxxxx>
>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>> ---
>>  arch/powerpc/platforms/powernv/memtrace.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/platforms/powernv/memtrace.c 
>> b/arch/powerpc/platforms/powernv/memtrace.c
>> index fdd48f1a39f7..d84d09c56af9 100644
>> --- a/arch/powerpc/platforms/powernv/memtrace.c
>> +++ b/arch/powerpc/platforms/powernv/memtrace.c
>> @@ -70,6 +70,7 @@ static int change_memblock_state(struct memory_block *mem, 
>> void *arg)
>>      return 0;
>>  }
>>  
>> +/* called with device_hotplug_lock held */
>>  static bool memtrace_offline_pages(u32 nid, u64 start_pfn, u64 nr_pages)
>>  {
>>      u64 end_pfn = start_pfn + nr_pages - 1;
>> @@ -111,6 +112,7 @@ static u64 memtrace_alloc_node(u32 nid, u64 size)
>>      end_pfn = round_down(end_pfn - nr_pages, nr_pages);
>>  
>>      for (base_pfn = end_pfn; base_pfn > start_pfn; base_pfn -= nr_pages) {
>> +            lock_device_hotplug();
> 
> Why not grab the lock before the for loop? That way we can avoid bad cases 
> like a
> large node being scanned for a small number of pages (nr_pages). Ideally we 
> need
> a cond_resched() in the loop, but I guess offline_pages() has one.

Yes, it does.

I can move it out of the loop, thanks!

> 
> Acked-by: Balbir Singh <bsingharora@xxxxxxxxx>
> 


-- 

Thanks,

David / dhildenb

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