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

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Date:   Thu, 12 Jan 2017 10:41:01 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, walken@...gle.com,
        boqun.feng@...il.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        npiggin@...il.com
Subject: Re: [PATCH v4 04/15] lockdep: Add a function building a chain
 between two classes

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
> >