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

[David Hildenbrand <david@redhat.com>]

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@kernel.crashing.org>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Rashmica Gupta <rashmica.g@gmail.com>
>> Cc: Balbir Singh <bsingharora@gmail.com>
>> Cc: Michael Neuling <mikey@neuling.org>
>> Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
>> Reviewed-by: Rashmica Gupta <rashmica.g@gmail.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  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@gmail.com>
> 


-- 

Thanks,

David / dhildenb