Re: [PATCH] mm/vmstat: fix divide error at __fragmentation_index

[<jiang.biao2@zte.com.cn>]

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> > On 08/03/2017 09:59 AM, Wen Yang wrote:



> > From: Jiang Biao <jiang.biao2@zte.com.cn>
> > 
> > When order is -1 or too big, *1UL << order* will be 0, which will
> > cause divide error like this,
> > 
> >     divide error: 0000 [#1] SMP
> >     Call Trace:
>>      [<ffffffff81168423>] compaction_suitable+0x63/0xc0
>> ...
> The trace seems to be from an old and non-mainline kernel, as it's the
> same as you reported here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=196555
> 
> In current mainline it seems to me that all callers of
> __fragmentation_index() will only do so with a valid order.
> 
> I wouldn't mind making a non-hotpath code more robust, but probably in a
> more obvious and self-reporting/documented way e.g. something like
> 
> if (WARN_ON_ONCE(order >= MAX_ORDER))
>     return 0
> 
yes, I noticed that, I'll send a new patch for that.




> > @@ -870,6 +870,9 @@ static int __fragmentation_index(unsigned int order, struct contig_page_info *in
> >  {
> >      unsigned long requested = 1UL << order
> >  
> > +        if (!requested)
> > +                return 0
> 
> Seems the indentation is broken here (spaces vs tabs).
I'll fix that.

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