Re: [PATCH 1/8] lockdep: fix recursive read lock validation

Peter Zijlstra
2008-04-29T14:57:43Z

On Tue, 2008-04-29 at 15:16 +0200, Bart Van Assche wrote:
> On Tue, Apr 29, 2008 at 2:57 PM, Gautham R Shenoy <ego@in.ibm.com> wrote:
> > Subject: lockdep: fix recursive read lock validation
> > This means that the following sequence is now invalid, whereas previously
> > it was considered valid:
> >
> > rlock(a); rlock(b); runlock(b); runlock(a)
> > rlock(b); rlock(a);
>
> Why are you marking this sequence as invalid ? Although it can be
> debated whether it is good programming practice to be inconsistent
> about the order of read-locking, the above sequence can't be involved
> in a deadlock.

Not for pure read locks, but when you add write locks to it, it does get
deadlocky. Lockdep does not keep separate chains for read and write
locks.