On 04/22/2016 05:04 AM, Peter Zijlstra wrote:
The only reason for the current code is to make GCC emit only the "LOCK XADD" instruction on x86 (and not do a pointless extra ADD on the result), do so nicer.Signed-off-by: Peter Zijlstra (Intel)<pet...@infradead.org> --- kernel/locking/qrwlock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/locking/qrwlock.c +++ b/kernel/locking/qrwlock.c @@ -93,7 +93,7 @@ void queued_read_lock_slowpath(struct qr * that accesses can't leak upwards out of our subsequent critical * section in the case that the lock is currently held for write. */ - cnts = atomic_add_return_acquire(_QR_BIAS,&lock->cnts) - _QR_BIAS; + cnts = atomic_fetch_add_acquire(_QR_BIAS,&lock->cnts); rspin_until_writer_unlock(lock, cnts); /*
Thanks for taking out this weirdness in the code. Acked-by: Waiman Long <waiman.l...@hpe.com>
