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Message-ID: <1464977394.3289.13.camel@j-VirtualBox>
Date: Fri, 03 Jun 2016 11:09:54 -0700
From: Jason Low <jason.low2@....com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...hat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Richard Henderson <rth@...ddle.net>,
Ivan Kokshaysky <ink@...assic.park.msu.ru>,
Matt Turner <mattst88@...il.com>,
Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Terry Rudd <terry.rudd@....com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Arnd Bergmann <arnd@...db.de>,
Christoph Lameter <cl@...ux.com>,
Davidlohr Bueso <dave@...olabs.net>,
Waiman Long <Waiman.Long@....com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Peter Hurley <peter@...leysoftware.com>,
Jason Low <jason.low2@...com>
Subject: Re: [RFC][PATCH 0/7] locking/rwsem: Convert rwsem count to
atomic_long_t
On Fri, 2016-06-03 at 10:04 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
>
> > On Mon, May 16, 2016 at 06:12:25PM -0700, Linus Torvalds wrote:
> > > On Mon, May 16, 2016 at 5:37 PM, Jason Low <jason.low2@....com> wrote:
> > > >
> > > > This rest of the series converts the rwsem count variable to an atomic_long_t
> > > > since it is used it as an atomic variable. This allows us to also remove
> > > > the rwsem_atomic_{add,update} abstraction and reduce 100+ lines of code.
> > >
> > > I would suggest you merge all the "remove rwsem_atomic_{add,update}"
> > > patches into a single patch.
> > >
> > > I don't see the advantage to splitting those up by architecture, and
> > > it does add noise to the series.
> > >
> > > Other than that it all looks fine to me.
> >
> > OK, done.
> >
> > ---
> > Subject: locking,rwsem: Remove rwsem_atomic_add() and rwsem_atomic_update()
> > From: Jason Low <jason.low2@....com>
> > Date: Mon, 16 May 2016 17:38:02 -0700
>
> So I tried to pick up this series, and it broke the Alpha and IA64 builds:
>
> /home/mingo/tip/arch/ia64/include/asm/rwsem.h: In function '___down_write':
> /home/mingo/tip/arch/ia64/include/asm/rwsem.h:58:7: error: incompatible types when
> assigning to type 'long int' from type 'atomic_long_t'
> old = sem->count;
> ^
>
> home/mingo/tip/arch/alpha/include/asm/rwsem.h: In function '__down_read':
> /home/mingo/tip/arch/alpha/include/asm/rwsem.h:28:11: error: incompatible types
> when assigning to type 'long int' from type 'atomic_long_t'
> oldcount = sem->count;
Right, we would also need to convert the sem->count usages in those
architectures to use atomic_long_read(), ect...
---
Subject: [PATCH] locking/rwsem: Convert rwsem->count to atomic_long_t
Convert the rwsem count variable to an atomic_long_t since we use it
as an atomic variable. This also allows us to remove the
rwsem_atomic_{add,update} "abstraction" which would now be an unnecesary
level of indirection. In follow up patches, we also remove the
rwsem_atomic_{add,update} definitions across the various architectures.
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Jason Low <jason.low2@....com>
---
arch/alpha/include/asm/rwsem.h | 26 +++++++++++++-------------
arch/ia64/include/asm/rwsem.h | 20 ++++++++++----------
include/asm-generic/rwsem.h | 6 +++---
include/linux/rwsem.h | 6 +++---
kernel/locking/rwsem-xadd.c | 32 +++++++++++++++++---------------
5 files changed, 46 insertions(+), 44 deletions(-)
diff --git a/arch/alpha/include/asm/rwsem.h b/arch/alpha/include/asm/rwsem.h
index 0131a70..9b66688 100644
--- a/arch/alpha/include/asm/rwsem.h
+++ b/arch/alpha/include/asm/rwsem.h
@@ -25,8 +25,8 @@ static inline void __down_read(struct rw_semaphore *sem)
{
long oldcount;
#ifndef CONFIG_SMP
- oldcount = sem->count;
- sem->count += RWSEM_ACTIVE_READ_BIAS;
+ oldcount = atomic_long_read(&sem->count);
+ atomic_long_add(RWSEM_ACTIVE_READ_BIAS, &sem->count);
#else
long temp;
__asm__ __volatile__(
@@ -52,13 +52,13 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
{
long old, new, res;
- res = sem->count;
+ res = atomic_long_read(&sem->count);
do {
new = res + RWSEM_ACTIVE_READ_BIAS;
if (new <= 0)
break;
old = res;
- res = cmpxchg(&sem->count, old, new);
+ res = atomic_long_cmpxchg(&sem->count, old, new);
} while (res != old);
return res >= 0 ? 1 : 0;
}
@@ -67,8 +67,8 @@ static inline long ___down_write(struct rw_semaphore *sem)
{
long oldcount;
#ifndef CONFIG_SMP
- oldcount = sem->count;
- sem->count += RWSEM_ACTIVE_WRITE_BIAS;
+ oldcount = atomic_long_read(&sem->count);
+ atomic_long_add(RWSEM_ACTIVE_WRITE_BIAS, &sem->count);
#else
long temp;
__asm__ __volatile__(
@@ -106,7 +106,7 @@ static inline int __down_write_killable(struct rw_semaphore *sem)
*/
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
- long ret = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
+ long ret = atomic_long_cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
if (ret == RWSEM_UNLOCKED_VALUE)
return 1;
@@ -117,8 +117,8 @@ static inline void __up_read(struct rw_semaphore *sem)
{
long oldcount;
#ifndef CONFIG_SMP
- oldcount = sem->count;
- sem->count -= RWSEM_ACTIVE_READ_BIAS;
+ oldcount = atomic_long_read(&sem->count);
+ atomic_long_add(-RWSEM_ACTIVE_READ_BIAS, &sem->count);
#else
long temp;
__asm__ __volatile__(
@@ -142,8 +142,8 @@ static inline void __up_write(struct rw_semaphore *sem)
{
long count;
#ifndef CONFIG_SMP
- sem->count -= RWSEM_ACTIVE_WRITE_BIAS;
- count = sem->count;
+ atomic_long_add(-RWSEM_ACTIVE_WRITE_BIAS, &sem->count);
+ count = atomic_long_read(&sem->count);
#else
long temp;
__asm__ __volatile__(
@@ -171,8 +171,8 @@ static inline void __downgrade_write(struct rw_semaphore *sem)
{
long oldcount;
#ifndef CONFIG_SMP
- oldcount = sem->count;
- sem->count -= RWSEM_WAITING_BIAS;
+ oldcount = atomic_long_read(&sem->count);
+ atomic_long_add(-RWSEM_WAITING_BIAS, &sem->count);
#else
long temp;
__asm__ __volatile__(
diff --git a/arch/ia64/include/asm/rwsem.h b/arch/ia64/include/asm/rwsem.h
index 8b23e07..72c37bb 100644
--- a/arch/ia64/include/asm/rwsem.h
+++ b/arch/ia64/include/asm/rwsem.h
@@ -55,9 +55,9 @@ ___down_write (struct rw_semaphore *sem)
long old, new;
do {
- old = sem->count;
+ old = atomic_long_read(&sem->count);
new = old + RWSEM_ACTIVE_WRITE_BIAS;
- } while (cmpxchg_acq(&sem->count, old, new) != old);
+ } while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
return old;
}
@@ -100,9 +100,9 @@ __up_write (struct rw_semaphore *sem)
long old, new;
do {
- old = sem->count;
+ old = atomic_long_read(&sem->count);
new = old - RWSEM_ACTIVE_WRITE_BIAS;
- } while (cmpxchg_rel(&sem->count, old, new) != old);
+ } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
@@ -115,8 +115,8 @@ static inline int
__down_read_trylock (struct rw_semaphore *sem)
{
long tmp;
- while ((tmp = sem->count) >= 0) {
- if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) {
+ while ((tmp = atomic_long_read(&sem->count)) >= 0) {
+ if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
return 1;
}
}
@@ -129,8 +129,8 @@ __down_read_trylock (struct rw_semaphore *sem)
static inline int
__down_write_trylock (struct rw_semaphore *sem)
{
- long tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE,
- RWSEM_ACTIVE_WRITE_BIAS);
+ long tmp = atomic_long_cmpxchg_acquire(&sem->count,
+ RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
return tmp == RWSEM_UNLOCKED_VALUE;
}
@@ -143,9 +143,9 @@ __downgrade_write (struct rw_semaphore *sem)
long old, new;
do {
- old = sem->count;
+ old = atomic_long_read(&sem->count);
new = old - RWSEM_WAITING_BIAS;
- } while (cmpxchg_rel(&sem->count, old, new) != old);
+ } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
if (old < 0)
rwsem_downgrade_wake(sem);
diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index 3fc94a0..a3a93ec 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -41,8 +41,8 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
{
long tmp;
- while ((tmp = sem->count) >= 0) {
- if (tmp == cmpxchg_acquire(&sem->count, tmp,
+ while ((tmp = atomic_long_read(&sem->count)) >= 0) {
+ if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
tmp + RWSEM_ACTIVE_READ_BIAS)) {
return 1;
}
@@ -79,7 +79,7 @@ static inline int __down_write_trylock(struct rw_semaphore *sem)
{
long tmp;
- tmp = cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
+ tmp = atomic_long_cmpxchg_acquire(&sem->count, RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
return tmp == RWSEM_UNLOCKED_VALUE;
}
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index d37fbb3..cb4d4aa 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -26,7 +26,7 @@ struct rw_semaphore;
#else
/* All arch specific implementations share the same struct */
struct rw_semaphore {
- long count;
+ atomic_long_t count;
struct list_head wait_list;
raw_spinlock_t wait_lock;
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
@@ -54,7 +54,7 @@ extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
/* In all implementations count != 0 means locked */
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
- return sem->count != 0;
+ return atomic_long_read(&sem->count) != 0;
}
#endif
@@ -74,7 +74,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
#endif
#define __RWSEM_INITIALIZER(name) \
- { .count = RWSEM_UNLOCKED_VALUE, \
+ { .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE), \
.wait_list = LIST_HEAD_INIT((name).wait_list), \
.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
__RWSEM_OPT_INIT(name) \
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index b957da7..63b40a5 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -80,7 +80,7 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map(&sem->dep_map, name, key, 0);
#endif
- sem->count = RWSEM_UNLOCKED_VALUE;
+ atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
raw_spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
@@ -153,10 +153,11 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
if (wake_type != RWSEM_WAKE_READ_OWNED) {
adjustment = RWSEM_ACTIVE_READ_BIAS;
try_reader_grant:
- oldcount = rwsem_atomic_update(adjustment, sem) - adjustment;
+ oldcount = atomic_long_add_return(adjustment, &sem->count) - adjustment;
+
if (unlikely(oldcount < RWSEM_WAITING_BIAS)) {
/* A writer stole the lock. Undo our reader grant. */
- if (rwsem_atomic_update(-adjustment, sem) &
+ if (atomic_long_sub_return(adjustment, &sem->count) &
RWSEM_ACTIVE_MASK)
goto out;
/* Last active locker left. Retry waking readers. */
@@ -186,7 +187,7 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
adjustment -= RWSEM_WAITING_BIAS;
if (adjustment)
- rwsem_atomic_add(adjustment, sem);
+ atomic_long_add(adjustment, &sem->count);
next = sem->wait_list.next;
loop = woken;
@@ -233,7 +234,7 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
list_add_tail(&waiter.list, &sem->wait_list);
/* we're now waiting on the lock, but no longer actively locking */
- count = rwsem_atomic_update(adjustment, sem);
+ count = atomic_long_add_return(adjustment, &sem->count);
/* If there are no active locks, wake the front queued process(es).
*
@@ -282,7 +283,8 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
RWSEM_ACTIVE_WRITE_BIAS :
RWSEM_ACTIVE_WRITE_BIAS + RWSEM_WAITING_BIAS;
- if (cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, count) == RWSEM_WAITING_BIAS) {
+ if (atomic_long_cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, count)
+ == RWSEM_WAITING_BIAS) {
rwsem_set_owner(sem);
return true;
}
@@ -296,13 +298,13 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
*/
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
{
- long old, count = READ_ONCE(sem->count);
+ long old, count = atomic_long_read(&sem->count);
while (true) {
if (!(count == 0 || count == RWSEM_WAITING_BIAS))
return false;
- old = cmpxchg_acquire(&sem->count, count,
+ old = atomic_long_cmpxchg_acquire(&sem->count, count,
count + RWSEM_ACTIVE_WRITE_BIAS);
if (old == count) {
rwsem_set_owner(sem);
@@ -324,7 +326,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
rcu_read_lock();
owner = READ_ONCE(sem->owner);
if (!owner) {
- long count = READ_ONCE(sem->count);
+ long count = atomic_long_read(&sem->count);
/*
* If sem->owner is not set, yet we have just recently entered the
* slowpath with the lock being active, then there is a possibility
@@ -375,7 +377,7 @@ bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
* held by readers. Check the counter to verify the
* state.
*/
- count = READ_ONCE(sem->count);
+ count = atomic_long_read(&sem->count);
return (count == 0 || count == RWSEM_WAITING_BIAS);
}
@@ -460,7 +462,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
WAKE_Q(wake_q);
/* undo write bias from down_write operation, stop active locking */
- count = rwsem_atomic_update(-RWSEM_ACTIVE_WRITE_BIAS, sem);
+ count = atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS, &sem->count);
/* do optimistic spinning and steal lock if possible */
if (rwsem_optimistic_spin(sem))
@@ -483,7 +485,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
/* we're now waiting on the lock, but no longer actively locking */
if (waiting) {
- count = READ_ONCE(sem->count);
+ count = atomic_long_read(&sem->count);
/*
* If there were already threads queued before us and there are
@@ -505,7 +507,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
}
} else
- count = rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
+ count = atomic_long_add_return(RWSEM_WAITING_BIAS, &sem->count);
/* wait until we successfully acquire the lock */
set_current_state(state);
@@ -521,7 +523,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
schedule();
set_current_state(state);
- } while ((count = sem->count) & RWSEM_ACTIVE_MASK);
+ } while ((count = atomic_long_read(&sem->count)) & RWSEM_ACTIVE_MASK);
raw_spin_lock_irq(&sem->wait_lock);
}
@@ -536,7 +538,7 @@ out_nolock:
raw_spin_lock_irq(&sem->wait_lock);
list_del(&waiter.list);
if (list_empty(&sem->wait_list))
- rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem);
+ atomic_long_add(-RWSEM_WAITING_BIAS, &sem->count);
else
__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
--
2.1.4
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