aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
-rw-r--r--ChangeLog46
-rw-r--r--NEWS11
-rw-r--r--include/atomic.h16
-rw-r--r--nptl/pthread_spin_init.c3
-rw-r--r--nptl/pthread_spin_lock.c71
-rw-r--r--nptl/pthread_spin_trylock.c54
-rw-r--r--nptl/pthread_spin_unlock.c6
-rw-r--r--sysdeps/aarch64/atomic-machine.h1
-rw-r--r--sysdeps/aarch64/nptl/pthread_spin_lock.c24
-rw-r--r--sysdeps/alpha/atomic-machine.h3
-rw-r--r--sysdeps/arm/atomic-machine.h1
-rw-r--r--sysdeps/arm/nptl/pthread_spin_lock.c23
-rw-r--r--sysdeps/hppa/nptl/pthread_spin_lock.c23
-rw-r--r--sysdeps/i386/atomic-machine.h1
-rw-r--r--sysdeps/ia64/atomic-machine.h3
-rw-r--r--sysdeps/m68k/coldfire/atomic-machine.h3
-rw-r--r--sysdeps/m68k/m680x0/m68020/atomic-machine.h3
-rw-r--r--sysdeps/m68k/nptl/pthread_spin_lock.c24
-rw-r--r--sysdeps/microblaze/atomic-machine.h3
-rw-r--r--sysdeps/microblaze/nptl/pthread_spin_lock.c24
-rw-r--r--sysdeps/mips/atomic-machine.h13
-rw-r--r--sysdeps/mips/nptl/pthread_spin_lock.c23
-rw-r--r--sysdeps/nios2/nptl/pthread_spin_lock.c24
-rw-r--r--sysdeps/powerpc/powerpc32/atomic-machine.h1
-rw-r--r--sysdeps/powerpc/powerpc64/atomic-machine.h1
-rw-r--r--sysdeps/s390/atomic-machine.h2
-rw-r--r--sysdeps/sparc/sparc32/atomic-machine.h3
-rw-r--r--sysdeps/sparc/sparc32/sparcv9/atomic-machine.h3
-rw-r--r--sysdeps/sparc/sparc64/atomic-machine.h3
-rw-r--r--sysdeps/tile/tilegx/atomic-machine.h1
-rw-r--r--sysdeps/tile/tilepro/atomic-machine.h1
-rw-r--r--sysdeps/unix/sysv/linux/hppa/atomic-machine.h3
-rw-r--r--sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h3
-rw-r--r--sysdeps/unix/sysv/linux/nios2/atomic-machine.h3
-rw-r--r--sysdeps/unix/sysv/linux/sh/atomic-machine.h3
-rw-r--r--sysdeps/x86_64/atomic-machine.h1
36 files changed, 226 insertions, 205 deletions
diff --git a/ChangeLog b/ChangeLog
index 4b90a00dc6..820c928948 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,49 @@
+2017-06-06 Stefan Liebler <stli@linux.vnet.ibm.com>
+
+ * NEWS: Mention new spinlock implementation.
+ * include/atomic.h:
+ (__atomic_val_bysize): Cast type to omit volatile qualifier.
+ (atomic_exchange_acq): Likewise.
+ (atomic_load_relaxed): Likewise.
+ (ATOMIC_EXCHANGE_USES_CAS): Check definition.
+ * nptl/pthread_spin_init.c (pthread_spin_init):
+ Use atomic_store_relaxed.
+ * nptl/pthread_spin_lock.c (pthread_spin_lock):
+ Use C11-like atomic macros.
+ * nptl/pthread_spin_trylock.c (pthread_spin_trylock):
+ Likewise.
+ * nptl/pthread_spin_unlock.c (pthread_spin_unlock):
+ Use atomic_store_release.
+ * sysdeps/aarch64/nptl/pthread_spin_lock.c: Delete File.
+ * sysdeps/arm/nptl/pthread_spin_lock.c: Likewise.
+ * sysdeps/hppa/nptl/pthread_spin_lock.c: Likewise.
+ * sysdeps/m68k/nptl/pthread_spin_lock.c: Likewise.
+ * sysdeps/microblaze/nptl/pthread_spin_lock.c: Likewise.
+ * sysdeps/mips/nptl/pthread_spin_lock.c: Likewise.
+ * sysdeps/nios2/nptl/pthread_spin_lock.c: Likewise.
+ * sysdeps/aarch64/atomic-machine.h (ATOMIC_EXCHANGE_USES_CAS): Define.
+ * sysdeps/alpha/atomic-machine.h: Likewise.
+ * sysdeps/arm/atomic-machine.h: Likewise.
+ * sysdeps/i386/atomic-machine.h: Likewise.
+ * sysdeps/ia64/atomic-machine.h: Likewise.
+ * sysdeps/m68k/coldfire/atomic-machine.h: Likewise.
+ * sysdeps/m68k/m680x0/m68020/atomic-machine.h: Likewise.
+ * sysdeps/microblaze/atomic-machine.h: Likewise.
+ * sysdeps/mips/atomic-machine.h: Likewise.
+ * sysdeps/powerpc/powerpc32/atomic-machine.h: Likewise.
+ * sysdeps/powerpc/powerpc64/atomic-machine.h: Likewise.
+ * sysdeps/s390/atomic-machine.h: Likewise.
+ * sysdeps/sparc/sparc32/atomic-machine.h: Likewise.
+ * sysdeps/sparc/sparc32/sparcv9/atomic-machine.h: Likewise.
+ * sysdeps/sparc/sparc64/atomic-machine.h: Likewise.
+ * sysdeps/tile/tilegx/atomic-machine.h: Likewise.
+ * sysdeps/tile/tilepro/atomic-machine.h: Likewise.
+ * sysdeps/unix/sysv/linux/hppa/atomic-machine.h: Likewise.
+ * sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h: Likewise.
+ * sysdeps/unix/sysv/linux/nios2/atomic-machine.h: Likewise.
+ * sysdeps/unix/sysv/linux/sh/atomic-machine.h: Likewise.
+ * sysdeps/x86_64/atomic-machine.h: Likewise.
+
2017-06-05 H.J. Lu <hongjiu.lu@intel.com>
* sysdeps/x86/cacheinfo.c (intel_check_word): Accept cpu_features
diff --git a/NEWS b/NEWS
index 608538f77f..991ee63f7c 100644
--- a/NEWS
+++ b/NEWS
@@ -80,6 +80,17 @@ Version 2.26
* The stack_t type no longer has the name struct sigaltstack. This changes
the C++ name mangling for interfaces involving this type.
+* The synchronization that pthread_spin_unlock performs has been changed
+ to now be equivalent to a C11 atomic store with release memory order to
+ the spin lock's memory location. This ensures correct synchronization
+ for the spin lock's operations and critical sections protected by a spin
+ lock. Previously, several (but not all) architectures used stronger
+ synchronization (e.g., containing what is often called a full barrier).
+ This change can improve performance, but may affect odd fringe uses of
+ spin locks that depend on the previous behavior (e.g., using spin locks
+ as atomic variables to try to implement Dekker's mutual exclusion
+ algorithm).
+
Security related changes:
* The DNS stub resolver limits the advertised UDP buffer size to 1200 bytes,
diff --git a/include/atomic.h b/include/atomic.h
index 7f326400c3..d002b117bf 100644
--- a/include/atomic.h
+++ b/include/atomic.h
@@ -54,7 +54,7 @@
and following args. */
#define __atomic_val_bysize(pre, post, mem, ...) \
({ \
- __typeof (*mem) __atg1_result; \
+ __typeof ((__typeof (*(mem))) *(mem)) __atg1_result; \
if (sizeof (*mem) == 1) \
__atg1_result = pre##_8_##post (mem, __VA_ARGS__); \
else if (sizeof (*mem) == 2) \
@@ -162,9 +162,9 @@
/* Store NEWVALUE in *MEM and return the old value. */
#ifndef atomic_exchange_acq
# define atomic_exchange_acq(mem, newvalue) \
- ({ __typeof (*(mem)) __atg5_oldval; \
+ ({ __typeof ((__typeof (*(mem))) *(mem)) __atg5_oldval; \
__typeof (mem) __atg5_memp = (mem); \
- __typeof (*(mem)) __atg5_value = (newvalue); \
+ __typeof ((__typeof (*(mem))) *(mem)) __atg5_value = (newvalue); \
\
do \
__atg5_oldval = *__atg5_memp; \
@@ -668,7 +668,7 @@ void __atomic_link_error (void);
# ifndef atomic_load_relaxed
# define atomic_load_relaxed(mem) \
- ({ __typeof (*(mem)) __atg100_val; \
+ ({ __typeof ((__typeof (*(mem))) *(mem)) __atg100_val; \
__asm ("" : "=r" (__atg100_val) : "0" (*(mem))); \
__atg100_val; })
# endif
@@ -818,4 +818,12 @@ void __atomic_link_error (void);
# define atomic_spin_nop() do { /* nothing */ } while (0)
#endif
+/* ATOMIC_EXCHANGE_USES_CAS is non-zero if atomic_exchange operations
+ are implemented based on a CAS loop; otherwise, this is zero and we assume
+ that the atomic_exchange operations could provide better performance
+ than a CAS loop. */
+#ifndef ATOMIC_EXCHANGE_USES_CAS
+# error ATOMIC_EXCHANGE_USES_CAS has to be defined.
+#endif
+
#endif /* atomic.h */
diff --git a/nptl/pthread_spin_init.c b/nptl/pthread_spin_init.c
index 01dec5eea4..fe3091377e 100644
--- a/nptl/pthread_spin_init.c
+++ b/nptl/pthread_spin_init.c
@@ -22,6 +22,7 @@
int
pthread_spin_init (pthread_spinlock_t *lock, int pshared)
{
- *lock = 0;
+ /* Relaxed MO is fine because this is an initializing store. */
+ atomic_store_relaxed (lock, 0);
return 0;
}
diff --git a/nptl/pthread_spin_lock.c b/nptl/pthread_spin_lock.c
index 4d03b7893a..682af80240 100644
--- a/nptl/pthread_spin_lock.c
+++ b/nptl/pthread_spin_lock.c
@@ -19,27 +19,35 @@
#include <atomic.h>
#include "pthreadP.h"
-/* A machine-specific version can define SPIN_LOCK_READS_BETWEEN_CMPXCHG
- to the number of plain reads that it's optimal to spin on between uses
- of atomic_compare_and_exchange_val_acq. If spinning forever is optimal
- then use -1. If no plain reads here would ever be optimal, use 0. */
-#ifndef SPIN_LOCK_READS_BETWEEN_CMPXCHG
-# warning machine-dependent file should define SPIN_LOCK_READS_BETWEEN_CMPXCHG
-# define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-#endif
-
int
pthread_spin_lock (pthread_spinlock_t *lock)
{
- /* atomic_exchange usually takes less instructions than
- atomic_compare_and_exchange. On the other hand,
- atomic_compare_and_exchange potentially generates less bus traffic
- when the lock is locked.
- We assume that the first try mostly will be successful, and we use
- atomic_exchange. For the subsequent tries we use
- atomic_compare_and_exchange. */
- if (atomic_exchange_acq (lock, 1) == 0)
+ int val = 0;
+
+ /* We assume that the first try mostly will be successful, thus we use
+ atomic_exchange if it is not implemented by a CAS loop (we also assume
+ that atomic_exchange can be faster if it succeeds, see
+ ATOMIC_EXCHANGE_USES_CAS). Otherwise, we use a weak CAS and not an
+ exchange so we bail out after the first failed attempt to change the
+ state. For the subsequent attempts we use atomic_compare_and_exchange
+ after we observe that the lock is not acquired.
+ See also comment in pthread_spin_trylock.
+ We use acquire MO to synchronize-with the release MO store in
+ pthread_spin_unlock, and thus ensure that prior critical sections
+ happen-before this critical section. */
+#if ! ATOMIC_EXCHANGE_USES_CAS
+ /* Try to acquire the lock with an exchange instruction as this architecture
+ has such an instruction and we assume it is faster than a CAS.
+ The acquisition succeeds if the lock is not in an acquired state. */
+ if (__glibc_likely (atomic_exchange_acquire (lock, 1) == 0))
return 0;
+#else
+ /* Try to acquire the lock with a CAS instruction as this architecture
+ has no exchange instruction. The acquisition succeeds if the lock is not
+ acquired. */
+ if (__glibc_likely (atomic_compare_exchange_weak_acquire (lock, &val, 1)))
+ return 0;
+#endif
do
{
@@ -47,23 +55,26 @@ pthread_spin_lock (pthread_spinlock_t *lock)
to cmpxchg is not a good idea on many targets as that will force
expensive memory synchronizations among processors and penalize other
running threads.
- On the other hand, we do want to update memory state on the local core
- once in a while to avoid spinning indefinitely until some event that
- will happen to update local memory as a side-effect. */
- if (SPIN_LOCK_READS_BETWEEN_CMPXCHG >= 0)
+ There is no technical reason for throwing in a CAS every now and then,
+ and so far we have no evidence that it can improve performance.
+ If that would be the case, we have to adjust other spin-waiting loops
+ elsewhere, too!
+ Thus we use relaxed MO reads until we observe the lock to not be
+ acquired anymore. */
+ do
{
- int wait = SPIN_LOCK_READS_BETWEEN_CMPXCHG;
+ /* TODO Back-off. */
- while (*lock != 0 && wait > 0)
- --wait;
- }
- else
- {
- while (*lock != 0)
- ;
+ atomic_spin_nop ();
+
+ val = atomic_load_relaxed (lock);
}
+ while (val != 0);
+
+ /* We need acquire memory order here for the same reason as mentioned
+ for the first try to lock the spinlock. */
}
- while (atomic_compare_and_exchange_val_acq (lock, 1, 0) != 0);
+ while (!atomic_compare_exchange_weak_acquire (lock, &val, 1));
return 0;
}
diff --git a/nptl/pthread_spin_trylock.c b/nptl/pthread_spin_trylock.c
index 593bba3ed8..83921b06b8 100644
--- a/nptl/pthread_spin_trylock.c
+++ b/nptl/pthread_spin_trylock.c
@@ -23,5 +23,57 @@
int
pthread_spin_trylock (pthread_spinlock_t *lock)
{
- return atomic_exchange_acq (lock, 1) ? EBUSY : 0;
+ /* For the spin try lock, we have the following possibilities:
+
+ 1) If we assume that trylock will most likely succeed in practice:
+ * We just do an exchange.
+
+ 2) If we want to bias towards cases where trylock succeeds, but don't
+ rule out contention:
+ * If exchange is not implemented by a CAS loop, and exchange is faster
+ than CAS, do an exchange.
+ * If exchange is implemented by a CAS loop, use a weak CAS and not an
+ exchange so we bail out after the first failed attempt to change the state.
+
+ 3) If we expect contention to be likely:
+ * If CAS always brings the cache line into an exclusive state even if the
+ spinlock is already acquired, then load the value first with
+ atomic_load_relaxed and test if lock is not acquired. Then do 2).
+
+ We assume that 2) is the common case, and that this won't be slower than
+ 1) in the common case.
+
+ We use acquire MO to synchronize-with the release MO store in
+ pthread_spin_unlock, and thus ensure that prior critical sections
+ happen-before this critical section. */
+#if ! ATOMIC_EXCHANGE_USES_CAS
+ /* Try to acquire the lock with an exchange instruction as this architecture
+ has such an instruction and we assume it is faster than a CAS.
+ The acquisition succeeds if the lock is not in an acquired state. */
+ if (atomic_exchange_acquire (lock, 1) == 0)
+ return 0;
+#else
+ /* Try to acquire the lock with a CAS instruction as this architecture
+ has no exchange instruction. The acquisition succeeds if the lock is not
+ acquired. */
+ do
+ {
+ int val = 0;
+ if (atomic_compare_exchange_weak_acquire (lock, &val, 1))
+ return 0;
+ }
+ /* atomic_compare_exchange_weak_acquire can fail spuriously. Whereas
+ C++11 and C11 make it clear that trylock operations can fail spuriously,
+ POSIX does not explicitly specify this; it only specifies that failing
+ synchronization operations do not need to have synchronization effects
+ themselves, but a spurious failure is something that could contradict a
+ happens-before established earlier (e.g., that we need to observe that
+ the lock is acquired). Therefore, we emulate a strong CAS by simply
+ checking with a relaxed MO load that the lock is really acquired before
+ returning EBUSY; the additional overhead this may cause is on the slow
+ path. */
+ while (atomic_load_relaxed (lock) == 0);
+#endif
+
+ return EBUSY;
}
diff --git a/nptl/pthread_spin_unlock.c b/nptl/pthread_spin_unlock.c
index 5fd73e578b..f83b69639a 100644
--- a/nptl/pthread_spin_unlock.c
+++ b/nptl/pthread_spin_unlock.c
@@ -23,7 +23,9 @@
int
pthread_spin_unlock (pthread_spinlock_t *lock)
{
- atomic_full_barrier ();
- *lock = 0;
+ /* The atomic_store_release synchronizes-with the atomic_exchange_acquire
+ or atomic_compare_exchange_weak_acquire in pthread_spin_lock /
+ pthread_spin_trylock. */
+ atomic_store_release (lock, 0);
return 0;
}
diff --git a/sysdeps/aarch64/atomic-machine.h b/sysdeps/aarch64/atomic-machine.h
index a5d2213d83..eb59a5b94c 100644
--- a/sysdeps/aarch64/atomic-machine.h
+++ b/sysdeps/aarch64/atomic-machine.h
@@ -38,6 +38,7 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 1
+#define ATOMIC_EXCHANGE_USES_CAS 0
/* Compare and exchange.
For all "bool" routines, we return FALSE if exchange succesful. */
diff --git a/sysdeps/aarch64/nptl/pthread_spin_lock.c b/sysdeps/aarch64/nptl/pthread_spin_lock.c
deleted file mode 100644
index fcfcb40215..0000000000
--- a/sysdeps/aarch64/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,24 +0,0 @@
-/* Copyright (C) 2008-2017 Free Software Foundation, Inc.
-
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public License as
- published by the Free Software Foundation; either version 2.1 of the
- License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/alpha/atomic-machine.h b/sysdeps/alpha/atomic-machine.h
index 06e93f2ddb..2cb2290837 100644
--- a/sysdeps/alpha/atomic-machine.h
+++ b/sysdeps/alpha/atomic-machine.h
@@ -45,6 +45,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
#ifdef UP
# define __MB /* nothing */
diff --git a/sysdeps/arm/atomic-machine.h b/sysdeps/arm/atomic-machine.h
index eeac7f0dbd..c22d05b766 100644
--- a/sysdeps/arm/atomic-machine.h
+++ b/sysdeps/arm/atomic-machine.h
@@ -35,6 +35,7 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define ATOMIC_EXCHANGE_USES_CAS 1
void __arm_link_error (void);
diff --git a/sysdeps/arm/nptl/pthread_spin_lock.c b/sysdeps/arm/nptl/pthread_spin_lock.c
deleted file mode 100644
index 037b3b82a0..0000000000
--- a/sysdeps/arm/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,23 +0,0 @@
-/* Copyright (C) 2008-2017 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library. If not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/hppa/nptl/pthread_spin_lock.c b/sysdeps/hppa/nptl/pthread_spin_lock.c
deleted file mode 100644
index 14f36a69dc..0000000000
--- a/sysdeps/hppa/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,23 +0,0 @@
-/* Copyright (C) 2005-2017 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library. If not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/i386/atomic-machine.h b/sysdeps/i386/atomic-machine.h
index 77759f7634..0e24200617 100644
--- a/sysdeps/i386/atomic-machine.h
+++ b/sysdeps/i386/atomic-machine.h
@@ -56,6 +56,7 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define ATOMIC_EXCHANGE_USES_CAS 0
#define atomic_compare_and_exchange_val_acq(mem, newval, oldval) \
diff --git a/sysdeps/ia64/atomic-machine.h b/sysdeps/ia64/atomic-machine.h
index ecf97500b4..f04ac05446 100644
--- a/sysdeps/ia64/atomic-machine.h
+++ b/sysdeps/ia64/atomic-machine.h
@@ -46,6 +46,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 0
+
#define __arch_compare_and_exchange_bool_8_acq(mem, newval, oldval) \
(abort (), 0)
diff --git a/sysdeps/m68k/coldfire/atomic-machine.h b/sysdeps/m68k/coldfire/atomic-machine.h
index 9aeb993487..d2e4a1f15d 100644
--- a/sysdeps/m68k/coldfire/atomic-machine.h
+++ b/sysdeps/m68k/coldfire/atomic-machine.h
@@ -53,6 +53,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* The only basic operation needed is compare and exchange. */
#define atomic_compare_and_exchange_val_acq(mem, newval, oldval) \
({ __typeof (mem) __gmemp = (mem); \
diff --git a/sysdeps/m68k/m680x0/m68020/atomic-machine.h b/sysdeps/m68k/m680x0/m68020/atomic-machine.h
index 00dc22d79d..83238f51de 100644
--- a/sysdeps/m68k/m680x0/m68020/atomic-machine.h
+++ b/sysdeps/m68k/m680x0/m68020/atomic-machine.h
@@ -47,6 +47,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
#define __arch_compare_and_exchange_val_8_acq(mem, newval, oldval) \
({ __typeof (*(mem)) __ret; \
__asm __volatile ("cas%.b %0,%2,%1" \
diff --git a/sysdeps/m68k/nptl/pthread_spin_lock.c b/sysdeps/m68k/nptl/pthread_spin_lock.c
deleted file mode 100644
index 62795f4cd2..0000000000
--- a/sysdeps/m68k/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,24 +0,0 @@
-/* Copyright (C) 2010-2017 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Maxim Kuvyrkov <maxim@codesourcery.com>, 2010.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library. If not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/microblaze/atomic-machine.h b/sysdeps/microblaze/atomic-machine.h
index dc5309c430..d73c69d46b 100644
--- a/sysdeps/microblaze/atomic-machine.h
+++ b/sysdeps/microblaze/atomic-machine.h
@@ -38,6 +38,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* Microblaze does not have byte and halfword forms of load and reserve and
store conditional. So for microblaze we stub out the 8- and 16-bit forms. */
diff --git a/sysdeps/microblaze/nptl/pthread_spin_lock.c b/sysdeps/microblaze/nptl/pthread_spin_lock.c
deleted file mode 100644
index fcfcb40215..0000000000
--- a/sysdeps/microblaze/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,24 +0,0 @@
-/* Copyright (C) 2008-2017 Free Software Foundation, Inc.
-
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public License as
- published by the Free Software Foundation; either version 2.1 of the
- License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/mips/atomic-machine.h b/sysdeps/mips/atomic-machine.h
index 54c182b38b..16fef6b797 100644
--- a/sysdeps/mips/atomic-machine.h
+++ b/sysdeps/mips/atomic-machine.h
@@ -92,7 +92,15 @@ typedef uintmax_t uatomic_max_t;
have no assembly alternative available and want to avoid the __sync_*
builtins if at all possible. */
-#define USE_ATOMIC_COMPILER_BUILTINS 1
+# define USE_ATOMIC_COMPILER_BUILTINS 1
+
+/* MIPS is an LL/SC machine. However, XLP has a direct atomic exchange
+ instruction which will be used by __atomic_exchange_n. */
+# ifdef _MIPS_ARCH_XLP
+# define ATOMIC_EXCHANGE_USES_CAS 0
+# else
+# define ATOMIC_EXCHANGE_USES_CAS 1
+# endif
/* Compare and exchange.
For all "bool" routines, we return FALSE if exchange succesful. */
@@ -213,7 +221,8 @@ typedef uintmax_t uatomic_max_t;
/* This implementation using inline assembly will be removed once glibc
requires GCC 4.8 or later to build. */
-#define USE_ATOMIC_COMPILER_BUILTINS 0
+# define USE_ATOMIC_COMPILER_BUILTINS 0
+# define ATOMIC_EXCHANGE_USES_CAS 1
/* Compare and exchange. For all of the "xxx" routines, we expect a
"__prev" and a "__cmp" variable to be provided by the enclosing scope,
diff --git a/sysdeps/mips/nptl/pthread_spin_lock.c b/sysdeps/mips/nptl/pthread_spin_lock.c
deleted file mode 100644
index 19d87a5861..0000000000
--- a/sysdeps/mips/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,23 +0,0 @@
-/* Copyright (C) 2012-2017 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library. If not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/nios2/nptl/pthread_spin_lock.c b/sysdeps/nios2/nptl/pthread_spin_lock.c
deleted file mode 100644
index b203469508..0000000000
--- a/sysdeps/nios2/nptl/pthread_spin_lock.c
+++ /dev/null
@@ -1,24 +0,0 @@
-/* pthread spin-lock implementation for Nios II.
- Copyright (C) 2005-2017 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library. If not, see
- <http://www.gnu.org/licenses/>. */
-
-#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
-
-/* We can't use the normal "#include <nptl/pthread_spin_lock.c>" because
- it will resolve to this very file. Using "sysdeps/.." as reference to the
- top level directory does the job. */
-#include <sysdeps/../nptl/pthread_spin_lock.c>
diff --git a/sysdeps/powerpc/powerpc32/atomic-machine.h b/sysdeps/powerpc/powerpc32/atomic-machine.h
index 20d5e85683..96c7d81359 100644
--- a/sysdeps/powerpc/powerpc32/atomic-machine.h
+++ b/sysdeps/powerpc/powerpc32/atomic-machine.h
@@ -35,6 +35,7 @@
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define ATOMIC_EXCHANGE_USES_CAS 1
/*
* The 32-bit exchange_bool is different on powerpc64 because the subf
diff --git a/sysdeps/powerpc/powerpc64/atomic-machine.h b/sysdeps/powerpc/powerpc64/atomic-machine.h
index 40c308e210..46df488b3c 100644
--- a/sysdeps/powerpc/powerpc64/atomic-machine.h
+++ b/sysdeps/powerpc/powerpc64/atomic-machine.h
@@ -35,6 +35,7 @@
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define ATOMIC_EXCHANGE_USES_CAS 1
/* The 32-bit exchange_bool is different on powerpc64 because the subf
does signed 64-bit arithmetic while the lwarx is 32-bit unsigned
diff --git a/sysdeps/s390/atomic-machine.h b/sysdeps/s390/atomic-machine.h
index 690d2e3065..adaca40798 100644
--- a/sysdeps/s390/atomic-machine.h
+++ b/sysdeps/s390/atomic-machine.h
@@ -67,6 +67,8 @@ typedef uintmax_t uatomic_max_t;
# define __HAVE_64B_ATOMICS 0
#endif
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* Implement some of the non-C11 atomic macros from include/atomic.h
with help of the C11 atomic builtins. The other non-C11 atomic macros
are using the macros defined here. */
diff --git a/sysdeps/sparc/sparc32/atomic-machine.h b/sysdeps/sparc/sparc32/atomic-machine.h
index acd029ea34..a2fe8485b4 100644
--- a/sysdeps/sparc/sparc32/atomic-machine.h
+++ b/sysdeps/sparc/sparc32/atomic-machine.h
@@ -50,6 +50,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* We have no compare and swap, just test and set.
The following implementation contends on 64 global locks
diff --git a/sysdeps/sparc/sparc32/sparcv9/atomic-machine.h b/sysdeps/sparc/sparc32/sparcv9/atomic-machine.h
index 7f7895e57b..2b36dfc94d 100644
--- a/sysdeps/sparc/sparc32/sparcv9/atomic-machine.h
+++ b/sysdeps/sparc/sparc32/sparcv9/atomic-machine.h
@@ -47,6 +47,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 0
+
#define __arch_compare_and_exchange_val_8_acq(mem, newval, oldval) \
(abort (), (__typeof (*mem)) 0)
diff --git a/sysdeps/sparc/sparc64/atomic-machine.h b/sysdeps/sparc/sparc64/atomic-machine.h
index 44a43ff0f5..72009329c3 100644
--- a/sysdeps/sparc/sparc64/atomic-machine.h
+++ b/sysdeps/sparc/sparc64/atomic-machine.h
@@ -47,6 +47,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
#define __arch_compare_and_exchange_val_8_acq(mem, newval, oldval) \
(abort (), (__typeof (*mem)) 0)
diff --git a/sysdeps/tile/tilegx/atomic-machine.h b/sysdeps/tile/tilegx/atomic-machine.h
index 6345251afd..e77f6707b0 100644
--- a/sysdeps/tile/tilegx/atomic-machine.h
+++ b/sysdeps/tile/tilegx/atomic-machine.h
@@ -31,6 +31,7 @@
#endif
#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define ATOMIC_EXCHANGE_USES_CAS 0
/* Pick appropriate 8- or 4-byte instruction. */
#define __atomic_update(mem, v, op) \
diff --git a/sysdeps/tile/tilepro/atomic-machine.h b/sysdeps/tile/tilepro/atomic-machine.h
index 33a8b85bbd..45e36de1e4 100644
--- a/sysdeps/tile/tilepro/atomic-machine.h
+++ b/sysdeps/tile/tilepro/atomic-machine.h
@@ -23,6 +23,7 @@
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define ATOMIC_EXCHANGE_USES_CAS 0
/* 32-bit integer compare-and-exchange. */
static __inline __attribute__ ((always_inline))
diff --git a/sysdeps/unix/sysv/linux/hppa/atomic-machine.h b/sysdeps/unix/sysv/linux/hppa/atomic-machine.h
index 2cd22352b1..59581bd4bc 100644
--- a/sysdeps/unix/sysv/linux/hppa/atomic-machine.h
+++ b/sysdeps/unix/sysv/linux/hppa/atomic-machine.h
@@ -39,6 +39,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* prev = *addr;
if (prev == old)
*addr = new;
diff --git a/sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h b/sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h
index 6755a056f4..1daac514a9 100644
--- a/sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h
+++ b/sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h
@@ -39,6 +39,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* The only basic operation needed is compare and exchange. */
/* For ColdFire we'll have to trap into the kernel mode anyway,
so trap from the library rather then from the kernel wrapper. */
diff --git a/sysdeps/unix/sysv/linux/nios2/atomic-machine.h b/sysdeps/unix/sysv/linux/nios2/atomic-machine.h
index 6111ccf886..d4dd025603 100644
--- a/sysdeps/unix/sysv/linux/nios2/atomic-machine.h
+++ b/sysdeps/unix/sysv/linux/nios2/atomic-machine.h
@@ -34,6 +34,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
#define __arch_compare_and_exchange_val_8_acq(mem, newval, oldval) \
(abort (), (__typeof (*mem)) 0)
#define __arch_compare_and_exchange_val_16_acq(mem, newval, oldval) \
diff --git a/sysdeps/unix/sysv/linux/sh/atomic-machine.h b/sysdeps/unix/sysv/linux/sh/atomic-machine.h
index 3c58b70c02..5a7e953ac4 100644
--- a/sysdeps/unix/sysv/linux/sh/atomic-machine.h
+++ b/sysdeps/unix/sysv/linux/sh/atomic-machine.h
@@ -47,6 +47,9 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 0
#define USE_ATOMIC_COMPILER_BUILTINS 0
+/* XXX Is this actually correct? */
+#define ATOMIC_EXCHANGE_USES_CAS 1
+
/* SH kernel has implemented a gUSA ("g" User Space Atomicity) support
for the user space atomicity. The atomicity macros use this scheme.
diff --git a/sysdeps/x86_64/atomic-machine.h b/sysdeps/x86_64/atomic-machine.h
index 2e8a9aad04..c454734001 100644
--- a/sysdeps/x86_64/atomic-machine.h
+++ b/sysdeps/x86_64/atomic-machine.h
@@ -59,6 +59,7 @@ typedef uintmax_t uatomic_max_t;
#define __HAVE_64B_ATOMICS 1
#define USE_ATOMIC_COMPILER_BUILTINS 1
+#define ATOMIC_EXCHANGE_USES_CAS 0
#define atomic_compare_and_exchange_val_acq(mem, newval, oldval) \
__sync_val_compare_and_swap (mem, oldval, newval)