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. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html