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Subject[tip:locking/core] locking/qrwlock: Use 'struct qrwlock' instead of 'struct __qrwlock'
Commit-ID:  e0d02285f16e8d5810f3d5d5e8a5886ca0015d3b
Gitweb: https://git.kernel.org/tip/e0d02285f16e8d5810f3d5d5e8a5886ca0015d3b
Author: Will Deacon <will.deacon@arm.com>
AuthorDate: Thu, 12 Oct 2017 13:20:47 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 25 Oct 2017 10:57:24 +0200

locking/qrwlock: Use 'struct qrwlock' instead of 'struct __qrwlock'

There's no good reason to keep the internal structure of struct qrwlock
hidden from qrwlock.h, particularly as it's actually needed for unlock
and ends up being abstracted independently behind the __qrwlock_write_byte()
function.

Stop pretending we can hide this stuff, and move the __qrwlock definition
into qrwlock, removing the __qrwlock_write_byte() nastiness and using the
same struct definition everywhere instead.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/asm-generic/qrwlock.h | 12 +-----------
include/asm-generic/qrwlock_types.h | 15 +++++++++++++--
kernel/locking/qrwlock.c | 26 ++------------------------
3 files changed, 16 insertions(+), 37 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 5092532..02c0a76 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -129,22 +129,12 @@ static inline void queued_read_unlock(struct qrwlock *lock)
}

/**
- * __qrwlock_write_byte - retrieve the write byte address of a queue rwlock
- * @lock : Pointer to queue rwlock structure
- * Return: the write byte address of a queue rwlock
- */
-static inline u8 *__qrwlock_write_byte(struct qrwlock *lock)
-{
- return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN);
-}
-
-/**
* 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)
{
- smp_store_release(__qrwlock_write_byte(lock), 0);
+ smp_store_release(&lock->wmode, 0);
}

/*
diff --git a/include/asm-generic/qrwlock_types.h b/include/asm-generic/qrwlock_types.h
index 0abc6b6..507f2dc 100644
--- a/include/asm-generic/qrwlock_types.h
+++ b/include/asm-generic/qrwlock_types.h
@@ -9,12 +9,23 @@
*/

typedef struct qrwlock {
- atomic_t cnts;
+ union {
+ atomic_t cnts;
+ struct {
+#ifdef __LITTLE_ENDIAN
+ u8 wmode; /* Writer mode */
+ u8 rcnts[3]; /* Reader counts */
+#else
+ u8 rcnts[3]; /* Reader counts */
+ u8 wmode; /* Writer mode */
+#endif
+ };
+ };
arch_spinlock_t wait_lock;
} arch_rwlock_t;

#define __ARCH_RW_LOCK_UNLOCKED { \
- .cnts = ATOMIC_INIT(0), \
+ { .cnts = ATOMIC_INIT(0), }, \
.wait_lock = __ARCH_SPIN_LOCK_UNLOCKED, \
}

diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index 2655f26..1af791e 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -23,26 +23,6 @@
#include <linux/spinlock.h>
#include <asm/qrwlock.h>

-/*
- * This internal data structure is used for optimizing access to some of
- * the subfields within the atomic_t cnts.
- */
-struct __qrwlock {
- union {
- atomic_t cnts;
- struct {
-#ifdef __LITTLE_ENDIAN
- u8 wmode; /* Writer mode */
- u8 rcnts[3]; /* Reader counts */
-#else
- u8 rcnts[3]; /* Reader counts */
- u8 wmode; /* Writer mode */
-#endif
- };
- };
- arch_spinlock_t lock;
-};
-
/**
* rspin_until_writer_unlock - inc reader count & spin until writer is gone
* @lock : Pointer to queue rwlock structure
@@ -125,10 +105,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
* or wait for a previous writer to go away.
*/
for (;;) {
- struct __qrwlock *l = (struct __qrwlock *)lock;
-
- if (!READ_ONCE(l->wmode) &&
- (cmpxchg_relaxed(&l->wmode, 0, _QW_WAITING) == 0))
+ if (!READ_ONCE(lock->wmode) &&
+ (cmpxchg_relaxed(&lock->wmode, 0, _QW_WAITING) == 0))
break;

cpu_relax();
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