Upadte.

2000-04-11  Ulrich Drepper  <drepper@redhat.com>

	* internals.h: Define MEMORY_BARRIER as empty if not defined already.
	* spinlock.c (__pthread_lock): Add memory barriers.
	(__pthread_unlock): Likewise.
	* sysdeps/alpha/pt-machine.h (MEMORY_BARRIER): Define using mb
	instruction.
	(RELEASE): Not needed anymore.
	(__compare_and_swap): Mark asm as modifying memory.
	* sysdeps/powerpc/pt-machine.h (sync): Remove.  Replace with definition
	of MEMORY_BARRIER.
	(__compare_and_swap): Use MEMORY_BARRIER instead of sync.
	* sysdeps/sparc/sparc32/pt-machine.h (RELEASE): Not needed anymore.
	(MEMORY_BARRIER): Define using stbar.
	* sysdeps/sparc/sparc64/pt-machine.h (MEMORY_BARRIER): Define using
	stbar.
	(__compare_and_swap): Use MEMORY_BARRIER to ensure ordering.
	Patch by Xavier Leroy <Xavier.Leroy@inria.fr> based on comments by
	Mike Burrows <m3b@pa.dec.com>.

1 files changed, 17 insertions, 0 deletions

diff --git a/linuxthreads/spinlock.c b/linuxthreads/spinlock.c
index b1a99d9..e1c40c0 100644
--- a/linuxthreads/spinlock.c
+++ b/linuxthreads/spinlock.c
@@ -54,6 +54,9 @@ void internal_function __pthread_lock(struct _pthread_fastlock * lock,
     if (self != NULL) {
       ASSERT(self->p_nextlock == NULL);
       THREAD_SETMEM(self, p_nextlock, (pthread_descr) oldstatus);
+      /* Make sure the store in p_nextlock completes before performing
+         the compare-and-swap */
+      MEMORY_BARRIER();
     }
   } while(! compare_and_swap(&lock->__status, oldstatus, newstatus,
                              &lock->__spinlock));
@@ -108,8 +111,17 @@ again:
       maxprio = thr->p_priority;
     }
     ptr = &(thr->p_nextlock);
+    /* Prevent reordering of the load of lock->__status above and the
+       load of *ptr below, as well as reordering of *ptr between
+       several iterations of the while loop.  Some processors (e.g.
+       multiprocessor Alphas) could perform such reordering even though
+       the loads are dependent. */
+    MEMORY_BARRIER();
     thr = *ptr;
   }
+  /* Prevent reordering of the load of lock->__status above and
+     thr->p_nextlock below */
+  MEMORY_BARRIER();
   /* Remove max prio thread from waiting list. */
   if (maxptr == (pthread_descr *) &lock->__status) {
     /* If max prio thread is at head, remove it with compare-and-swap
@@ -124,6 +136,9 @@ again:
     thr = *maxptr;
     *maxptr = thr->p_nextlock;
   }
+  /* Prevent reordering of store to *maxptr above and store to thr->p_nextlock
+     below */
+  MEMORY_BARRIER();
   /* Wake up the selected waiting thread */
   thr->p_nextlock = NULL;
   restart(thr);
@@ -149,6 +164,8 @@ int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
   } else {
     res = 0;
   }
+  /* Prevent reordering of store to *ptr above and store to *spinlock below */
+  MEMORY_BARRIER();
   *spinlock = 0;
   return res;
 }