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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 /sysdeps/hppa/nptl/pthread_spin_unlock.c
parentdb2f6f4794f722eac43b4b831f41abfc784fcfb5 (diff)
hppa: fix pthread spinlock
URL: https://bugs.debian.org/725508
Diffstat (limited to 'sysdeps/hppa/nptl/pthread_spin_unlock.c')
-rw-r--r--sysdeps/hppa/nptl/pthread_spin_unlock.c24
1 files changed, 20 insertions, 4 deletions
diff --git a/sysdeps/hppa/nptl/pthread_spin_unlock.c b/sysdeps/hppa/nptl/pthread_spin_unlock.c
index 31162a7873..6e4d71ecf1 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;
}