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From: David Xu <davidxu@FreeBSD.org>
Date: Wed, 25 Aug 2010 03:14:32 +0000 (UTC)
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Subject: svn commit: r211794 - head/sys/kern
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Author: davidxu
Date: Wed Aug 25 03:14:32 2010
New Revision: 211794
URL: http://svn.freebsd.org/changeset/base/211794

Log:
  If a thread is removed from umtxq while sleeping, reset error code
  to zero, this gives userland a better indication that a thread needn't
  to be cancelled.

Modified:
  head/sys/kern/kern_umtx.c

Modified: head/sys/kern/kern_umtx.c
==============================================================================
--- head/sys/kern/kern_umtx.c	Wed Aug 25 02:09:07 2010	(r211793)
+++ head/sys/kern/kern_umtx.c	Wed Aug 25 03:14:32 2010	(r211794)
@@ -1059,8 +1059,10 @@ do_wait(struct thread *td, void *addr, u
 		umtxq_lock(&uq->uq_key);
 		for (;;) {
 			error = umtxq_sleep(uq, "uwait", tvtohz(&tv));
-			if (!(uq->uq_flags & UQF_UMTXQ))
+			if (!(uq->uq_flags & UQF_UMTXQ)) {
+				error = 0;
 				break;
+			}
 			if (error != ETIMEDOUT)
 				break;
 			umtxq_unlock(&uq->uq_key);
@@ -2404,25 +2406,14 @@ do_cv_wait(struct thread *td, struct uco
 		}
 	}
 
-	if (error != 0) {
-		if ((uq->uq_flags & UQF_UMTXQ) == 0) {
-			/*
-			 * If we concurrently got do_cv_signal()d
-			 * and we got an error or UNIX signals or a timeout,
-			 * then, perform another umtxq_signal to avoid
-			 * consuming the wakeup. This may cause supurious
-			 * wakeup for another thread which was just queued,
-			 * but SUSV3 explicitly allows supurious wakeup to
-			 * occur, and indeed a kernel based implementation
-			 * can not avoid it.
-			 */ 
-			if (!umtxq_signal(&uq->uq_key, 1))
-				error = 0;
-		}
+	if ((uq->uq_flags & UQF_UMTXQ) == 0)
+		error = 0;
+	else {
+		umtxq_remove(uq);
 		if (error == ERESTART)
 			error = EINTR;
 	}
-	umtxq_remove(uq);
+
 	umtxq_unlock(&uq->uq_key);
 	umtx_key_release(&uq->uq_key);
 	return (error);
@@ -2891,15 +2882,13 @@ do_sem_wait(struct thread *td, struct _u
 		}
 	}
 
-	if (error != 0) {
-		if ((uq->uq_flags & UQF_UMTXQ) == 0) {
-			if (!umtxq_signal(&uq->uq_key, 1))
-				error = 0;
-		}
+	if ((uq->uq_flags & UQF_UMTXQ) == 0)
+		error = 0;
+	else {
+		umtxq_remove(uq);
 		if (error == ERESTART)
 			error = EINTR;
 	}
-	umtxq_remove(uq);
 	umtxq_unlock(&uq->uq_key);
 	umtx_key_release(&uq->uq_key);
 	return (error);