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From: Arnd Bergmann <arnd@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>,
	Matthew Wilcox <willy@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Will Deacon <will@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Waiman Long <longman@redhat.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] qspinlock: use signed temporaries for cmpxchg
Date: Mon, 26 Oct 2020 17:57:51 +0100	[thread overview]
Message-ID: <20201026165807.3724647-1-arnd@kernel.org> (raw)

From: Arnd Bergmann <arnd@arndb.de>

When building with W=2, the build log is flooded with

include/asm-generic/qrwlock.h:65:56: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qrwlock.h:92:53: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qspinlock.h:68:55: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qspinlock.h:82:52: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]

The atomics are built on top of signed integers, but the caller
doesn't actually care. Just use signed types as well.

Fixes: 27df89689e25 ("locking/spinlocks: Remove an instruction from spin and write locks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/asm-generic/qrwlock.h   | 8 ++++----
 include/asm-generic/qspinlock.h | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 3aefde23dcea..84ce841ce735 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -37,7 +37,7 @@ extern void queued_write_lock_slowpath(struct qrwlock *lock);
  */
 static inline int queued_read_trylock(struct qrwlock *lock)
 {
-	u32 cnts;
+	int cnts;
 
 	cnts = atomic_read(&lock->cnts);
 	if (likely(!(cnts & _QW_WMASK))) {
@@ -56,7 +56,7 @@ static inline int queued_read_trylock(struct qrwlock *lock)
  */
 static inline int queued_write_trylock(struct qrwlock *lock)
 {
-	u32 cnts;
+	int cnts;
 
 	cnts = atomic_read(&lock->cnts);
 	if (unlikely(cnts))
@@ -71,7 +71,7 @@ static inline int queued_write_trylock(struct qrwlock *lock)
  */
 static inline void queued_read_lock(struct qrwlock *lock)
 {
-	u32 cnts;
+	int cnts;
 
 	cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
 	if (likely(!(cnts & _QW_WMASK)))
@@ -87,7 +87,7 @@ static inline void queued_read_lock(struct qrwlock *lock)
  */
 static inline void queued_write_lock(struct qrwlock *lock)
 {
-	u32 cnts = 0;
+	int cnts = 0;
 	/* Optimize for the unfair lock case where the fair flag is 0. */
 	if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
 		return;
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index 4fe7fd0fe834..d74b13825501 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -60,7 +60,7 @@ static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  */
 static __always_inline int queued_spin_trylock(struct qspinlock *lock)
 {
-	u32 val = atomic_read(&lock->val);
+	int val = atomic_read(&lock->val);
 
 	if (unlikely(val))
 		return 0;
@@ -77,7 +77,7 @@ extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  */
 static __always_inline void queued_spin_lock(struct qspinlock *lock)
 {
-	u32 val = 0;
+	int val = 0;
 
 	if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
 		return;
-- 
2.27.0


             reply	other threads:[~2020-10-26 16:58 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 16:57 Arnd Bergmann [this message]
2020-10-26 17:10 ` [PATCH] qspinlock: use signed temporaries for cmpxchg Peter Zijlstra
2020-10-26 18:03 ` Waiman Long
2020-10-27  7:47   ` Peter Zijlstra
2020-10-27  8:33     ` Arnd Bergmann
2020-10-27 10:32       ` Peter Zijlstra
2020-10-27 13:38         ` David Laight
2020-10-27 16:22         ` Arnd Bergmann
2020-10-27 17:34           ` Peter Zijlstra

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