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locking/spinlock, arch: Update and fix spin_unlock_wait() implementations

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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>
This commit is contained in:
Peter Zijlstra
2016-05-26 10:35:03 +02:00
committed by Ingo Molnar
parent b464d1270a
commit 726328d92a
20 changed files with 145 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
arch/mips/include/asm/spinlock.h
View File

@@ -12,6 +12,7 @@
#include <linux/compiler.h>
#include <asm/barrier.h>
#include <asm/processor.h>
#include <asm/compiler.h>
#include <asm/war.h>
@@ -48,8 +49,22 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
}
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
#define arch_spin_unlock_wait(x) \
while (arch_spin_is_locked(x)) { cpu_relax(); }
static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
{
u16 owner = READ_ONCE(lock->h.serving_now);
smp_rmb();
for (;;) {
arch_spinlock_t tmp = READ_ONCE(*lock);
if (tmp.h.serving_now == tmp.h.ticket ||
tmp.h.serving_now != owner)
break;
cpu_relax();
}
smp_acquire__after_ctrl_dep();
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{