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SubjectRe: [PATCH 1/1] lockdep: Kill held_lock->check and "int check" arg of __lock_acquire()
On Mon, Jan 13, 2014 at 06:28:33PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 13, 2014 at 06:06:09PM +0100, Oleg Nesterov wrote:
> > On 01/12, Oleg Nesterov wrote:
> > >
> > > The "int check" argument of lock_acquire() and held_lock->check
> > > are misleading and unneeded. This is only used as a boolean, 2
> > > denotes "true", everything else is "false". And this boolean is
> > > always equal to prove_locking.
> > >
> > > The only exception is __lockdep_no_validate__ which should make
> > > this condition "false" in validate_chain().
> >
> > And I missed mark_irqflags(),
> >
> > > @@ -3136,7 +3130,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
> > > hlock->holdtime_stamp = lockstat_clock();
> > > #endif
> > >
> > > - if (check == 2 && !mark_irqflags(curr, hlock))
> > > + if (prove_locking && !mark_irqflags(curr, hlock))
> > > return 0;
> >
> > This change is not right, at least it is not equivalent.
> >
> > And I just realized that rcu_lock_acquire() does lock_acquire(check => 1).
> > Probably we can mark rcu_lock_map's as __lockdep_no_validate__.
>
> Can't, RCU needs its own classes. Otherwise it cannot tell which version
> of the RCU read lock its holding at just that moment.

Just confirming this. RCU uses this to detected mismatches between
the rcu_read_lock() group and the rcu_dereference() group.

Thanx, Paul

> > Anything else I missed?
>
> Nothing springs to mind, but then, I totally missed the RCU thing too.
>
> At the very least we can reduce check to a single bit.
>



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