Hello Julian,
Can you please apply the attached patch ? The attached patch fixes the
assertion failure triggered by the tc18_semabuse test on Fedora 8. The
fix consists of removing a tl_assert() statement. In this case this is
OK, because what the tl_assert() statement was checking is that
sem_post() did not report an error. The assert statement was there
because if sem_post() returns an error, in theory some real data races
can be suppressed. However, sem_post() only reports an error (EINVAL)
in case its argument is not a valid semaphore, so there is no danger
of suppressing a real data race.
Bart Van Assche.
Index: exp-drd/drd_semaphore.c
===================================================================
--- exp-drd/drd_semaphore.c (revision 7405)
+++ exp-drd/drd_semaphore.c (working copy)
@@ -165,12 +165,15 @@
void semaphore_post_post(const DrdThreadId tid, const Addr semaphore,
const SizeT size, const Bool waited)
{
- /* Note: it is hard to implement the sem_post() wrapper correctly if */
- /* sem_post() can return an error code. The reason is that this would */
- /* require to detect whether sem_post() will fail before sem_post is */
- /* called -- p->vc may only be modified if the sem_post() call will */
- /* succeed. */
- tl_assert(waited);
+ /* Note: it is hard to implement the sem_post() wrapper correctly in */
+ /* case sem_post() returns an error code. This is because handling this */
+ /* case correctly requires restoring the vector clock associated with */
+ /* the semaphore to its original value here. In order to do that without */
+ /* introducing a race condition, extra locking has to be added around */
+ /* each semaphore call. Such extra locking would have to be added in */
+ /* drd_intercepts.c. However, it is hard to implement synchronization */
+ /* in drd_intercepts.c in a portable way without calling already */
+ /* redirected functions. */
}
void semaphore_thread_delete(const DrdThreadId threadid)
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