Index: sys/kern/kern_sig.c
===================================================================
--- sys/kern/kern_sig.c
+++ sys/kern/kern_sig.c
@@ -3300,6 +3300,87 @@
     CTLFLAG_MPSAFE, 0, 0, sysctl_kern_corefile, "A",
     "Process corefile name format string");
 
+/*
+ * If the core format has a %I in it, then we need to check
+ * for existing corefiles before defining a name.
+ * To do this we iterate over 0..num_cores to find a
+ * non-existing core file name to use. If all core files are
+ * already used we choose the oldest one.
+ */
+static int
+corefile_open_last(struct thread *td, char *name, int indexpos,
+    struct vnode **vpp)
+{
+	struct vnode *oldvp, *nextvp;
+	struct nameidata nd;
+	struct stat sb;
+	int error, i, flags, oflags, cmode;
+	time_t lastsec;
+
+	nextvp = oldvp = NULL;
+	cmode = S_IRUSR | S_IWUSR;
+	oflags = VN_OPEN_NOAUDIT | VN_OPEN_NAMECACHE |
+	    (capmode_coredump ? VN_OPEN_NOCAPCHECK : 0);
+
+	for (i = 0; i < num_cores; i++) {
+		struct vnode *vp;
+
+		flags = O_CREAT | FWRITE | O_NOFOLLOW;
+		name[indexpos] = '0' + i;
+
+		NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
+		error = vn_open_cred(&nd, &flags, cmode, oflags, td->td_ucred,
+		    NULL);
+		if (error != 0)
+			break;
+
+		vp = nd.ni_vp;
+		NDFREE(&nd, NDF_ONLY_PNBUF);
+		if ((flags & O_CREAT) == O_CREAT) {
+			nextvp = vp;
+			break;
+		}
+
+		error = vn_stat(vp, &sb, td->td_ucred, NOCRED, td);
+		if (error != 0) {
+			VOP_UNLOCK(vp, 0);
+			vn_close(vp, FWRITE, td->td_ucred, td);
+			break;
+		}
+
+		if (oldvp == NULL || lastsec >= sb.st_mtim.tv_sec) {
+			if (oldvp != NULL) {
+				VOP_UNLOCK(oldvp, 0);
+				vn_close(oldvp, FWRITE, td->td_ucred, td);
+			}
+			oldvp = vp;
+			lastsec = sb.st_mtim.tv_sec;
+		} else {
+			VOP_UNLOCK(vp, 0);
+			vn_close(vp, FWRITE, td->td_ucred, td);
+		}
+	}
+
+	if (oldvp != NULL) {
+		if (nextvp == NULL) {
+			nextvp = oldvp;
+		} else {
+			VOP_UNLOCK(oldvp, 0);
+			vn_close(oldvp, FWRITE, td->td_ucred, td);
+		}
+	}
+	if (error != 0) {
+		if (nextvp != NULL) {
+			VOP_UNLOCK(nextvp, 0);
+			vn_close(nextvp, FWRITE, td->td_ucred, td);
+		}
+	} else {
+		*vpp = nextvp;
+	}
+
+	return (error);
+}
+
 /*
  * corefile_open(comm, uid, pid, td, compress, vpp, namep)
  * Expand the name described in corefilename, using name, uid, and pid
@@ -3316,11 +3397,10 @@
 corefile_open(const char *comm, uid_t uid, pid_t pid, struct thread *td,
     int compress, struct vnode **vpp, char **namep)
 {
-	struct nameidata nd;
 	struct sbuf sb;
 	const char *format;
 	char *hostname, *name;
-	int indexpos, i, error, cmode, flags, oflags;
+	int indexpos, error, i;
 
 	hostname = NULL;
 	format = corefilename;
@@ -3386,48 +3466,39 @@
 	sbuf_finish(&sb);
 	sbuf_delete(&sb);
 
-	cmode = S_IRUSR | S_IWUSR;
-	oflags = VN_OPEN_NOAUDIT | VN_OPEN_NAMECACHE |
-	    (capmode_coredump ? VN_OPEN_NOCAPCHECK : 0);
-
-	/*
-	 * If the core format has a %I in it, then we need to check
-	 * for existing corefiles before returning a name.
-	 * To do this we iterate over 0..num_cores to find a
-	 * non-existing core file name to use.
-	 */
 	if (indexpos != -1) {
-		for (i = 0; i < num_cores; i++) {
-			flags = O_CREAT | O_EXCL | FWRITE | O_NOFOLLOW;
-			name[indexpos] = '0' + i;
-			NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
-			error = vn_open_cred(&nd, &flags, cmode, oflags,
-			    td->td_ucred, NULL);
-			if (error) {
-				if (error == EEXIST)
-					continue;
-				log(LOG_ERR,
-				    "pid %d (%s), uid (%u):  Path `%s' failed "
-				    "on initial open test, error = %d\n",
-				    pid, comm, uid, name, error);
-			}
-			goto out;
+		error = corefile_open_last(td, name, indexpos, vpp);
+		if (error != 0) {
+			log(LOG_ERR,
+			    "pid %d (%s), uid (%u):  Path `%s' failed "
+			    "on initial open test, error = %d\n",
+			    pid, comm, uid, name, error);
+		}
+	} else {
+		struct nameidata nd;
+		int cmode, flags, oflags;
+
+		cmode = S_IRUSR | S_IWUSR;
+		oflags = VN_OPEN_NOAUDIT | VN_OPEN_NAMECACHE |
+		    (capmode_coredump ? VN_OPEN_NOCAPCHECK : 0);
+		flags = O_CREAT | FWRITE | O_NOFOLLOW;
+
+		NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
+		error = vn_open_cred(&nd, &flags, cmode, oflags, td->td_ucred,
+		    NULL);
+		if (error == 0) {
+			*vpp = nd.ni_vp;
+			NDFREE(&nd, NDF_ONLY_PNBUF);
 		}
 	}
 
-	flags = O_CREAT | FWRITE | O_NOFOLLOW;
-	NDINIT(&nd, LOOKUP, NOFOLLOW, UIO_SYSSPACE, name, td);
-	error = vn_open_cred(&nd, &flags, cmode, oflags, td->td_ucred, NULL);
-out:
-	if (error) {
+	if (error != 0) {
 #ifdef AUDIT
 		audit_proc_coredump(td, name, error);
 #endif
 		free(name, M_TEMP);
 		return (error);
 	}
-	NDFREE(&nd, NDF_ONLY_PNBUF);
-	*vpp = nd.ni_vp;
 	*namep = name;
 	return (0);
 }