Messages in this thread | | | Date | Thu, 23 Jan 2014 11:07:51 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v10 1/4] qrwlock: A queue read/write lock implementation |
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On Wed, Jan 22, 2014 at 04:33:55PM -0500, Waiman Long wrote: > +/** > + * queue_read_unlock - release read lock of a queue rwlock > + * @lock : Pointer to queue rwlock structure > + */ > +static inline void queue_read_unlock(struct qrwlock *lock) > +{ > + /* > + * Atomically decrement the reader count > + */ > + atomic_sub(_QR_BIAS, &lock->cnts.rwa); > +} > + > +/** > + * queue_write_unlock - release write lock of a queue rwlock > + * @lock : Pointer to queue rwlock structure > + */ > +static inline void queue_write_unlock(struct qrwlock *lock) > +{ > + /* > + * If the writer field is atomic, it can be cleared directly. > + * Otherwise, an atomic subtraction will be used to clear it. > + */ > + if (__native_word(lock->cnts.writer)) > + smp_store_release(&lock->cnts.writer, 0); > + else > + atomic_sub(_QW_LOCKED, &lock->cnts.rwa); > +}
Both these unlocks miss a barrier; atomic_sub() doesn't imply any barrier what so ever.
The smp_store_release() does, but the other two are invalid release ops in generic.
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