Bother. Yet another semaphore bug. I don't think your patch is
correct, since it would decrement both count and waking with
(count=0, waking=0).
I think this is correct, though I didn't see whatever it was that
was triggering the problem.
r~
diff -rup 2.2.5/include/asm-alpha/semaphore-helper.h 2.2.5-axp/include/asm-alpha/semaphore-helper.h
--- 2.2.5/include/asm-alpha/semaphore-helper.h Thu Apr 8 09:01:52 1999
+++ 2.2.5-axp/include/asm-alpha/semaphore-helper.h Tue Apr 13 09:15:54 1999
@@ -50,7 +50,7 @@ waking_non_zero(struct semaphore *sem)
* 0 go to sleep
* -EINTR interrupted
*
- * We must undo the sem->count down_interruptible increment
+ * We must undo the sem->count down_interruptible decrement
* simultaneously and atomicly with the sem->waking adjustment,
* otherwise we can race with wake_one_more.
*
diff -rup 2.2.5/include/asm-alpha/semaphore.h 2.2.5-axp/include/asm-alpha/semaphore.h
--- 2.2.5/include/asm-alpha/semaphore.h Sun Apr 11 17:48:36 1999
+++ 2.2.5-axp/include/asm-alpha/semaphore.h Tue Apr 13 08:52:09 1999
@@ -115,42 +115,43 @@ extern inline int down_interruptible(str
extern inline int down_trylock(struct semaphore * sem)
{
- long ret, tmp, tmp2;
+ long ret, tmp, tmp2, sub;
/* "Equivalent" C. Note that we have to do this all without
(taken) branches in order to be a valid ll/sc sequence.
do {
tmp = ldq_l;
- ret = 0;
- tmp -= 1;
- if ((int)tmp < 0) // count
- break;
- if ((long)tmp < 0) // waking
- break;
- tmp += 0xffffffff00000000;
- ret = 1;
+ sub = 0x0000000100000000;
+ ret = ((int)tmp <= 0); // count <= 0 ?
+ // If we're subtracting one from count, we don't need
+ // one from waking and vice versa.
+ if ((int)tmp > 0) sub = 1; // count > 0 ?
+ if ((long)tmp >= 0) ret = 0; // waking >= 0 ?
+ if (ret) break;
+ tmp -= sub;
tmp = stq_c = tmp;
} while (tmp == 0);
*/
__asm__ __volatile__(
- "1: ldq_l %1,%3\n"
- " lda %0,0\n"
- " subl %1,1,%2\n"
- " subq %1,1,%1\n"
- " blt %2,2f\n"
- " blt %1,2f\n"
- " ldah %1,-32768(%1)\n"
- " ldah %1,-32768(%1)\n"
- " lda %0,1\n"
- " stq_c %1,%3\n"
+ "1: ldq_l %1,%4\n"
+ " lda %3,1\n"
+ " addl %1,0,%2\n"
+ " sll %3,32,%3\n"
+ " cmple %2,0,%0\n"
+ " cmovgt %2,1,%3\n"
+ " cmovge %1,0,%0\n"
+ " bne %0,2f\n"
+ " subq %1,%3,%1\n"
+ " stq_c %1,%4\n"
" beq %1,3f\n"
- "2: mb\n"
+ " mb\n"
+ "2:\n"
".section .text2,\"ax\"\n"
"3: br 1b\n"
".previous"
- : "=&r"(ret), "=&r"(tmp), "=&r"(tmp2)
+ : "=&r"(ret), "=&r"(tmp), "=&r"(tmp2), "=&r"(sub)
: "m"(*sem)
: "memory");
-
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