Re: [patch 2/16] list_head debugging

From: Rik van Riel (riel@conectiva.com.br)
Date: Fri Jun 14 2002 - 04:22:27 EST


On Mon, 10 Jun 2002, Jan Harkes wrote:
> On Mon, Jun 03, 2002 at 05:41:39PM -0300, Rik van Riel wrote:
> > > We've had this before, and it breaks some code that removes items from
> > > lists as follows,
> >
> > Such code is probably not SMP safe anyway.
>
> Where are you coming from with that comment?
>
> down(&semaphore);
>
> list_for_each(p, list)
> if (condition)
> list_del(p);
>
> up(&semaphore);
>
> Should be completely SMP safe,

Not if 'p' comes from the slab cache.

In that case 'p' can be re-allocated on another CPU
before we dereference ->next ...

regards,

Rik

-- 
Bravely reimplemented by the knights who say "NIH".

http://www.surriel.com/ http://distro.conectiva.com/

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