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SubjectRe: frequent softlockups with 3.10rc6.
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On Mon, 2013-06-24 at 12:51 -0400, Dave Jones wrote:
> On Mon, Jun 24, 2013 at 12:24:39PM -0400, Steven Rostedt wrote:
>
> > > Ah, this is the first victim of my new 'check sanity of nodes during list walks' patch.
> > > It's doing the same prev->next next->prev checking as list_add and friends.
> > > I'm looking at getting it into shape for a 3.12 merge after some other preparatory patches
> > > go into 3.11
> >
> > OK, and you may need to make an exception for the ring buffer. To do a
> > lockless swap out of the reader page for one of the pages in the buffer,
> > it uses the 2 LSB as flags. Notice the "next=ffff880243288001", that "1"
> > is a flag that states the next page is the "header" page (next to be
> > read). We use cmpxchg to update the pages to handle races between the
> > reader and writer.
>
> I just had a plumber come visit to replace my toilet.
> I think even he would say "dude, gross" about that hack.
>

Wow, that hack made you so sick you needed to replace your toilet?

Note, the idea of using the 2 LSB bits of pointers came from -rt. Where
we do the same with the rt_mutex owner.

-- Steve




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