Re: [PATCH] writeback: initialize m_dirty to avoid compile warning

[Shi, Yang]

On 11/18/2015 10:55 AM, Andrew Morton wrote:
> On Wed, 18 Nov 2015 10:39:23 -0800 "Shi, Yang" <yang.shi@xxxxxxxxxx> wrote:
>
> > On 11/18/2015 10:33 AM, Tejun Heo wrote:
> > > Hello,
> > >
> > > On Wed, Nov 18, 2015 at 10:27:32AM -0800, Shi, Yang wrote:
> > > > > This was the main reason the code was structured the way it is.  If
> > > > > cgroup writeback is not enabled, any derefs of mdtc variables should
> > > > > trigger warnings.  Ugh... I don't know.  Compiler really should be
> > > > > able to tell this much.
> > > >
> > > > Thanks for the explanation. It sounds like a compiler problem.
> > > >
> > > > If you think it is still good to cease the compile warning, maybe we could
> > >
> > > If this is gonna be a problem with new gcc versions, I don't think we
> > > have any other options. :(
> > >
> > > > just assign it to an insane value as what Andrew suggested, maybe
> > > > 0xdeadbeef.
> > >
> > > I'd just keep it at zero.  Whatever we do, the effect is gonna be
> > > difficult to track down - it's not gonna blow up in an obvious way.
> > > Can you please add a comment tho explaining that this is to work
> > > around compiler deficiency?
> >
> > Sure.
> >
> > Other than this, in v2, I will just initialize m_dirty since compiler
> > just reports it is uninitialized.
>
> gcc-4.4.4 and gcc-4.8.4 warn about all three variables.

It sounds 5.x is smarter :-)
> --- a/mm/page-writeback.c~writeback-initialize-m_dirty-to-avoid-compile-warning-fix
> +++ a/mm/page-writeback.c
> @@ -1542,7 +1542,9 @@ static void balance_dirty_pages(struct a
>   	for (;;) {
>   		unsigned long now = jiffies;
>   		unsigned long dirty, thresh, bg_thresh;
> -		unsigned long m_dirty = 0, m_thresh = 0, m_bg_thresh = 0;
> +		unsigned long m_dirty = 0;	/* stop bogus uninit warnings */
> +		unsigned long m_thresh = 0;
> +		unsigned long m_bg_thresh = 0;

Still need v2?

Thanks,
Yang

>   		/*
>   		 * Unstable writes are a feature of certain networked
> _

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