Messages in this thread | | | Date | Thu, 23 Jan 2014 12:12:07 -0500 | From | Waiman Long <> | Subject | Re: [PATCH v10 1/4] qrwlock: A queue read/write lock implementation |
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On 01/23/2014 05:07 AM, Peter Zijlstra wrote: > 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.
I thought that all atomic RMW instructions are memory barrier. If they are not, what kind of barrier should be added?
-Longman
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