Messages in this thread | | | Date | Mon, 09 Sep 2013 13:55:06 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without taking rename_lock |
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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
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