linux-kernel - [PATCH v4 5/8] locking/qrwlock: implement queue_write_unlock using smp_store

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Message-Id: <1438621351-15912-6-git-send-email-will.deacon@arm.com>
Date:	Mon,  3 Aug 2015 18:02:28 +0100
From:	Will Deacon <will.deacon@....com>
To:	linux-arch@...r.kernel.org
Cc:	Waiman.Long@...com, peterz@...radead.org,
	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	mingo@...nel.org, Will Deacon <will.deacon@....com>
Subject: [PATCH v4 5/8] locking/qrwlock: implement queue_write_unlock using smp_store_release

Since 536fa402221f ("compiler: Allow 1- and 2-byte smp_load_acquire()
and smp_store_release()"), smp_store_release supports byte accesses, so
use that in writer unlock and remove the conditional macro override.

Signed-off-by: Will Deacon <will.deacon@....com>
---
 arch/x86/include/asm/qrwlock.h | 10 ----------
 include/asm-generic/qrwlock.h  |  9 +--------
 2 files changed, 1 insertion(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/qrwlock.h b/arch/x86/include/asm/qrwlock.h
index a8810bf135ab..c537cbb038a7 100644
--- a/arch/x86/include/asm/qrwlock.h
+++ b/arch/x86/include/asm/qrwlock.h
@@ -2,16 +2,6 @@
 #define _ASM_X86_QRWLOCK_H
 
 #include <asm-generic/qrwlock_types.h>
-
-#ifndef CONFIG_X86_PPRO_FENCE
-#define queued_write_unlock queued_write_unlock
-static inline void queued_write_unlock(struct qrwlock *lock)
-{
-        barrier();
-        ACCESS_ONCE(*(u8 *)&lock->cnts) = 0;
-}
-#endif
-
 #include <asm-generic/qrwlock.h>
 
 #endif /* _ASM_X86_QRWLOCK_H */
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index deb9e8b0eb9e..eb673dde8879 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -134,21 +134,14 @@ static inline void queued_read_unlock(struct qrwlock *lock)
 	atomic_sub(_QR_BIAS, &lock->cnts);
 }
 
-#ifndef queued_write_unlock
 /**
  * queued_write_unlock - release write lock of a queue rwlock
  * @lock : Pointer to queue rwlock structure
  */
 static inline void queued_write_unlock(struct qrwlock *lock)
 {
-	/*
-	 * If the writer field is atomic, it can be cleared directly.
-	 * Otherwise, an atomic subtraction will be used to clear it.
-	 */
-	smp_mb__before_atomic();
-	atomic_sub(_QW_LOCKED, &lock->cnts);
+	smp_store_release((u8 *)&lock->cnts, 0);
 }
-#endif
 
 /*
  * Remapping rwlock architecture specific functions to the corresponding
-- 
2.1.4

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