• Peter Zijlstra's avatar
    locking/spinlock, arch: Update and fix spin_unlock_wait() implementations · 726328d9
    Peter Zijlstra authored
    This patch updates/fixes all spin_unlock_wait() implementations.
    
    The update is in semantics; where it previously was only a control
    dependency, we now upgrade to a full load-acquire to match the
    store-release from the spin_unlock() we waited on. This ensures that
    when spin_unlock_wait() returns, we're guaranteed to observe the full
    critical section we waited on.
    
    This fixes a number of spin_unlock_wait() users that (not
    unreasonably) rely on this.
    
    I also fixed a number of ticket lock versions to only wait on the
    current lock holder, instead of for a full unlock, as this is
    sufficient.
    
    Furthermore; again for ticket locks; I added an smp_rmb() in between
    the initial ticket load and the spin loop testing the current value
    because I could not convince myself the address dependency is
    sufficient, esp. if the loads are of different sizes.
    
    I'm more than happy to remove this smp_rmb() again if people are
    certain the address dependency does indeed work as expected.
    
    Note: PPC32 will be fixed independently
    Signed-off-by: 's avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: chris@zankel.net
    Cc: cmetcalf@mellanox.com
    Cc: davem@davemloft.net
    Cc: dhowells@redhat.com
    Cc: james.hogan@imgtec.com
    Cc: jejb@parisc-linux.org
    Cc: linux@armlinux.org.uk
    Cc: mpe@ellerman.id.au
    Cc: ralf@linux-mips.org
    Cc: realmz6@gmail.com
    Cc: rkuo@codeaurora.org
    Cc: rth@twiddle.net
    Cc: schwidefsky@de.ibm.com
    Cc: tony.luck@intel.com
    Cc: vgupta@synopsys.com
    Cc: ysato@users.sourceforge.jp
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: 's avatarIngo Molnar <mingo@kernel.org>
    726328d9
barrier.h 5.6 KB