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SubjectRe: 2.6.11-rc2-mm1
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
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