From 726328d92a42b6d4b76078e2659f43067f82c4e8 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 26 May 2016 10:35:03 +0200 Subject: 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) Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner 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 --- arch/tile/lib/spinlock_32.c | 6 ++++++ arch/tile/lib/spinlock_64.c | 6 ++++++ 2 files changed, 12 insertions(+) (limited to 'arch/tile') diff --git a/arch/tile/lib/spinlock_32.c b/arch/tile/lib/spinlock_32.c index 88c2a53362e7..076c6cc43113 100644 --- a/arch/tile/lib/spinlock_32.c +++ b/arch/tile/lib/spinlock_32.c @@ -76,6 +76,12 @@ void arch_spin_unlock_wait(arch_spinlock_t *lock) do { delay_backoff(iterations++); } while (READ_ONCE(lock->current_ticket) == curr); + + /* + * The TILE architecture doesn't do read speculation; therefore + * a control dependency guarantees a LOAD->{LOAD,STORE} order. + */ + barrier(); } EXPORT_SYMBOL(arch_spin_unlock_wait); diff --git a/arch/tile/lib/spinlock_64.c b/arch/tile/lib/spinlock_64.c index c8d1f94ff1fe..a4b5b2cbce93 100644 --- a/arch/tile/lib/spinlock_64.c +++ b/arch/tile/lib/spinlock_64.c @@ -76,6 +76,12 @@ void arch_spin_unlock_wait(arch_spinlock_t *lock) do { delay_backoff(iterations++); } while (arch_spin_current(READ_ONCE(lock->lock)) == curr); + + /* + * The TILE architecture doesn't do read speculation; therefore + * a control dependency guarantees a LOAD->{LOAD,STORE} order. + */ + barrier(); } EXPORT_SYMBOL(arch_spin_unlock_wait); -- cgit v1.2.3