locking/qspinlock: Clarify xchg_tail() ordering

While going over the code I noticed that xchg_tail() is a RELEASE but
had no obvious pairing commented.

It pairs with a somewhat unique address dependency through
decode_tail().

So the store-release of xchg_tail() is paired by the address
dependency of the load of xchg_tail followed by the dereference from
the pointer computed from that load.

The @old -> @prev transformation itself is pure, and therefore does
not depend on external state, so that is immaterial wrt. ordering.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Pan Xinhui <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions