locking/spinlock, arch: Update and fix spin_unlock_wait() implementations
authorPeter Zijlstra <peterz@infradead.org>
Thu, 26 May 2016 08:35:03 +0000 (10:35 +0200)
committerIngo Molnar <mingo@kernel.org>
Tue, 14 Jun 2016 09:55:15 +0000 (11:55 +0200)
commit726328d92a42b6d4b76078e2659f43067f82c4e8
tree6df3622839432fc698c4404cbb0a0922a1357251
parentb464d1270a8016edcf1fd20d77cefdecf9b0b73e
locking/spinlock, arch: Update and fix spin_unlock_wait() implementations

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: Peter 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: Ingo Molnar <mingo@kernel.org>
20 files changed:
arch/alpha/include/asm/spinlock.h
arch/arc/include/asm/spinlock.h
arch/arm/include/asm/spinlock.h
arch/blackfin/include/asm/spinlock.h
arch/hexagon/include/asm/spinlock.h
arch/ia64/include/asm/spinlock.h
arch/m32r/include/asm/spinlock.h
arch/metag/include/asm/spinlock.h
arch/mips/include/asm/spinlock.h
arch/mn10300/include/asm/spinlock.h
arch/parisc/include/asm/spinlock.h
arch/s390/include/asm/spinlock.h
arch/sh/include/asm/spinlock.h
arch/sparc/include/asm/spinlock_32.h
arch/sparc/include/asm/spinlock_64.h
arch/tile/lib/spinlock_32.c
arch/tile/lib/spinlock_64.c
arch/xtensa/include/asm/spinlock.h
include/asm-generic/barrier.h
include/linux/spinlock_up.h