linux-kernel - [PATCH 09/10] locking/qspinlock: Make queued_spin_unlock use smp_store

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Message-Id: <1522947547-24081-10-git-send-email-will.deacon@arm.com>
Date:   Thu,  5 Apr 2018 17:59:06 +0100
From:   Will Deacon <will.deacon@....com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org, peterz@...radead.org,
        mingo@...nel.org, boqun.feng@...il.com, paulmck@...ux.vnet.ibm.com,
        catalin.marinas@....com, Will Deacon <will.deacon@....com>
Subject: [PATCH 09/10] locking/qspinlock: Make queued_spin_unlock use smp_store_release

A qspinlock can be unlocked simply by writing zero to the locked byte.
This can be implemented in the generic code, so do that and remove the
arch-specific override for x86 in the !PV case.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Will Deacon <will.deacon@....com>
---
 arch/x86/include/asm/qspinlock.h | 17 ++++++-----------
 include/asm-generic/qspinlock.h  |  2 +-
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 90b0b0ed8161..cc77cbb01432 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -7,6 +7,12 @@
 #include <asm-generic/qspinlock_types.h>
 #include <asm/paravirt.h>
 
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __pv_init_lock_hash(void);
+extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock);
+
 #define	queued_spin_unlock queued_spin_unlock
 /**
  * queued_spin_unlock - release a queued spinlock
@@ -19,12 +25,6 @@ static inline void native_queued_spin_unlock(struct qspinlock *lock)
 	smp_store_release(&lock->locked, 0);
 }
 
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
-extern void __pv_init_lock_hash(void);
-extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
-extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock);
-
 static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 {
 	pv_queued_spin_lock_slowpath(lock, val);
@@ -40,11 +40,6 @@ static inline bool vcpu_is_preempted(long cpu)
 {
 	return pv_vcpu_is_preempted(cpu);
 }
-#else
-static inline void queued_spin_unlock(struct qspinlock *lock)
-{
-	native_queued_spin_unlock(lock);
-}
 #endif
 
 #ifdef CONFIG_PARAVIRT
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index b37b4ad7eb94..a8ed0a352d75 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -100,7 +100,7 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
 	/*
 	 * unlock() needs release semantics:
 	 */
-	(void)atomic_sub_return_release(_Q_LOCKED_VAL, &lock->val);
+	smp_store_release(&lock->locked, 0);
 }
 #endif
 
-- 
2.1.4