Messages in this thread | | | Date | Mon, 4 Jan 2010 18:03:08 -0800 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock() |
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On Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote: > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the > task structure, which happens to be a signed int. So this patch adds a > check for this counter being negative at the end of __rcu_read_unlock(). > This check is under CONFIG_PROVE_LOCKING, so can be thought of as being > part of lockdep. > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > kernel/rcutree_plugin.h | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index f11ebd4..e77cdf3 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -304,6 +304,9 @@ void __rcu_read_unlock(void) > if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 && > unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) > rcu_read_unlock_special(t); > +#ifdef CONFIG_PROVE_LOCKING > + WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); > +#endif /* #ifdef CONFIG_PROVE_LOCKING */ > } > EXPORT_SYMBOL_GPL(__rcu_read_unlock);
Given that you *already* need to access t->rcu_read_lock_nesting here, why not just do the test all the time? Ideally you could access t->rcu_read_lock_nesting once, decrement it, and test for both 0 and negative.
- Josh Triplett
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