Re: 2.6.11-rc2-mm1

[Jörn Engel]

On Tue, 25 January 2005 19:04:47 +0300, Evgeniy Polyakov wrote:
> On Tue, 2005-01-25 at 16:34 +0100, Bartlomiej Zolnierkiewicz wrote:
> 
> > Ugh, now think about that:
> > 
> > CPU0     CPU1
> > place1:   place2:
> > lock a      lock b
> > < guess what happens here :-) >
> > lock b      lock a
> > ...             ...
> 
> :) he-he, such place are in add and remove routings, and they can not be
> run simultaneously
> in different CPUs.

Makes my toenails curl.  Something fun I might write someday is a
statical (dead-)lock checker.  The design is very simple:

o Annotate code with the lock that could be taken.
o Whenever getting a lock B, write down something like "A->B" for
  every lock A we already have.
o Create a graph from the locking hierarchy obtained above.
o Look for cycles.

A cycle-free graph means that the code is deadlock-free.  In the
above, the graph surely has cycles.  You could argue that the checker
should be smarter, but then again - why should it?  Is there a
compelling reason why locking schemes as outlined above actually make
the code better?

Jörn

-- 
It does not matter how slowly you go, so long as you do not stop.
-- Confucius
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/