Re: [PATCH v4 1/1] dcache: Translating dentry into pathname withouttaking rename_lock

[Waiman Long]

On 09/09/2013 01:29 PM, Al Viro wrote:
> On Mon, Sep 09, 2013 at 12:18:13PM -0400, Waiman Long wrote:
> > +/**
> > + * read_seqbegin_or_lock - begin a sequence number check or locking block
> > + * lock: sequence lock
> > + * seq : sequence number to be checked
> > + *
> > + * First try it once optimistically without taking the lock. If that fails,
> > + * take the lock. The sequence number is also used as a marker for deciding
> > + * whether to be a reader (even) or writer (odd).
> > + * N.B. seq must be initialized to an even number to begin with.
> > + */
> > +static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
> > +{
> > +	if (!(*seq&  1)) {	/* Even */
> > +		*seq = read_seqbegin(lock);
> > +		rcu_read_lock();
> > +	} else			/* Odd */
> > +		write_seqlock(lock);
> > +}
> > +static inline int read_seqretry_or_unlock(seqlock_t *lock, int *seq)
> > +{
> > +	if (!(*seq&  1)) {	/* Even */
> > +		rcu_read_unlock();
> > +		if (read_seqretry(lock, *seq)) {
> > +			(*seq)++;	/* Take writer lock */
> > +			return 1;
> > +		}
> > +	} else			/* Odd */
> > +		write_sequnlock(lock);
> > +	return 0;
> > +}
> I'm not sure I like mixing rcu_read_lock() into that - d_path() and friends
> can do that themselves just fine (it needs to be taken when seq is even),
> and e.g. d_walk() doesn't need it at all.  Other than that, I'm OK with
> this variant.

I think rcu_read_lock() is needed to make sure that the dentry won't be 
freed as we don't take d_lock now.

-Longman
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/