Re: [PATCH v4 04/15] lockdep: Add a function building a chain between two classes

Byungchul Park
2017-01-12T01:46:00Z

On Tue, Jan 10, 2017 at 10:00:38PM +0100, Peter Zijlstra wrote:
> > +static inline int add_chain_cache_classes(unsigned int prev,
> > + unsigned int next,
> > + unsigned int irq_context,
> > + u64 chain_key)
> > +{
> > + struct hlist_head *hash_head = chainhashentry(chain_key);
> > + struct lock_chain *chain;
> > +
> > + /*
> > + * Allocate a new chain entry from the static array, and add
> > + * it to the hash:
> > + */
> > +
> > + /*
> > + * We might need to take the graph lock, ensure we've got IRQs
> > + * disabled to make this an IRQ-safe lock.. for recursion reasons
> > + * lockdep won't complain about its own locking errors.
> > + */
> > + if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> > + return 0;
> > +
> > + if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) {
> > + if (!debug_locks_off_graph_unlock())
> > + return 0;
> > +
> > + print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
> > + dump_stack();
> > + return 0;
> > + }
> > +
> > + chain = lock_chains + nr_lock_chains++;
> > + chain->chain_key = chain_key;
> > + chain->irq_context = irq_context;
> > + chain->depth = 2;
> > + if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
> > + chain->base = nr_chain_hlocks;
> > + nr_chain_hlocks += chain->depth;
> > + chain_hlocks[chain->base] = prev - 1;
> > + chain_hlocks[chain->base + 1] = next -1;
> > + }
>
> You didn't copy this part right. There is no error when >
> MAX_LOCKDEP_CHAIN_HLOCKS.

Oh my god! I am sorry. I missed it.

Thank you,
Byungchul

>
>
> > + hlist_add_head_rcu(&chain->entry, hash_head);
> > + debug_atomic_inc(chain_lookup_misses);
> > + inc_chains();
> > +
> > + return 1;
> > +}
> > +
> > static inline int add_chain_cache(struct task_struct *curr,
> > struct held_lock *hlock,
> > u64 chain_key)
> > --
> > 1.9.1
> >