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authorJohn David Anglin <dave.anglin@bell.net>2014-05-04 14:02:30 -0400
committerMike Frysinger <vapier@gentoo.org>2016-01-06 17:26:04 -0500
commitd7f914848b7d5e9b11bbffd1fecc4659d4acdc2d (patch)
treeb2d229d7551680a57ed3aba6086f941852a426fd
parentdb2f6f4794f722eac43b4b831f41abfc784fcfb5 (diff)
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hppa: fix pthread spinlock
URL: https://bugs.debian.org/725508
-rw-r--r--ChangeLog7
-rw-r--r--sysdeps/hppa/nptl/pthread_spin_init.c24
-rw-r--r--sysdeps/hppa/nptl/pthread_spin_unlock.c24
3 files changed, 47 insertions, 8 deletions
diff --git a/ChangeLog b/ChangeLog
index 72614feb821..acaf7a87a0a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2016-01-06 John David Anglin <dave.anglin@bell.net>
+
+ * sysdeps/hppa/nptl/pthread_spin_init.c (pthread_spin_init): Replace
+ asm stw with atomic_exchange_rel. Add explanatory comment.
+ * sysdeps/hppa/nptl/pthread_spin_unlock.c (pthread_spin_unlock):
+ Likewise.
+
2016-01-05 H.J. Lu <hongjiu.lu@intel.com>
[BZ #19122]
diff --git a/sysdeps/hppa/nptl/pthread_spin_init.c b/sysdeps/hppa/nptl/pthread_spin_init.c
index 729d53f26f7..2df0376d8b7 100644
--- a/sysdeps/hppa/nptl/pthread_spin_init.c
+++ b/sysdeps/hppa/nptl/pthread_spin_init.c
@@ -20,9 +20,25 @@
int
pthread_spin_init (pthread_spinlock_t *lock, int pshared)
{
- int tmp = 0;
- /* This should be a memory barrier to newer compilers */
- __asm__ __volatile__ ("stw,ma %1,0(%0)"
- : : "r" (lock), "r" (tmp) : "memory");
+ /* CONCURRENCTY NOTES:
+
+ The atomic_exchange_rel synchronizes-with the atomic_exhange_acq in
+ pthread_spin_lock.
+
+ On hppa we must not use a plain `stw` to reset the guard lock. This
+ has to do with the kernel compare-and-swap helper that is used to
+ implement all of the atomic operations.
+
+ The kernel CAS helper uses its own internal locks and that means that
+ to create a true happens-before relationship between any two threads,
+ the second thread must observe the internal lock having a value of 0
+ (it must attempt to take the lock with ldcw). This creates the
+ ordering required for a second thread to observe the effects of the
+ RMW of the kernel CAS helper in any other thread.
+
+ Therefore if a variable is used in an atomic macro it must always be
+ manipulated with atomic macros in order for memory ordering rules to
+ be preserved. */
+ atomic_exchange_rel (lock, 0);
return 0;
}
diff --git a/sysdeps/hppa/nptl/pthread_spin_unlock.c b/sysdeps/hppa/nptl/pthread_spin_unlock.c
index 31162a78738..6e4d71ecf16 100644
--- a/sysdeps/hppa/nptl/pthread_spin_unlock.c
+++ b/sysdeps/hppa/nptl/pthread_spin_unlock.c
@@ -20,9 +20,25 @@
int
pthread_spin_unlock (pthread_spinlock_t *lock)
{
- int tmp = 0;
- /* This should be a memory barrier to newer compilers */
- __asm__ __volatile__ ("stw,ma %1,0(%0)"
- : : "r" (lock), "r" (tmp) : "memory");
+ /* CONCURRENCTY NOTES:
+
+ The atomic_exchange_rel synchronizes-with the atomic_exhange_acq in
+ pthread_spin_lock.
+
+ On hppa we must not use a plain `stw` to reset the guard lock. This
+ has to do with the kernel compare-and-swap helper that is used to
+ implement all of the atomic operations.
+
+ The kernel CAS helper uses its own internal locks and that means that
+ to create a true happens-before relationship between any two threads,
+ the second thread must observe the internal lock having a value of 0
+ (it must attempt to take the lock with ldcw). This creates the
+ ordering required for a second thread to observe the effects of the
+ RMW of the kernel CAS helper in any other thread.
+
+ Therefore if a variable is used in an atomic macro it must always be
+ manipulated with atomic macros in order for memory ordering rules to
+ be preserved. */
+ atomic_exchange_rel (lock, 0);
return 0;
}