restorer: close log file before detaching from crtools

v2: it's toom risky to jump to address equal to line numbet (there could be
valid executable code). So now jump is done to 0 address and %sp encodes line
number (32 most significant bits) and error code (32 least significant bits).

There is a race between log close by process being restoring and opened file
desctriptors check in zdtm test suite - crtools can exit and compare file
descriptors before detached restored process will perform all the rest tasks
(including close of the log) and execute final system call:

 |--- dump/sleeping00/8578/dump.fd        2012-02-20 14:31:31.246096000 +0300
 |+++ dump/sleeping00/8578/restore.fd     2012-02-20 14:31:31.418095999 +0300
 |@@ -1,4 +1,5 @@
 |
 | 0 -> /dev/null
 | 1 -> /dev/null
 |+1023 -> /root/crtools/test/dump/sleeping00/8578/restore.log
 | 2 -> /dev/null

The solution is to close log in restorer before final command received. But
this leads to another problem: we have to inform somehow about possible errors
afterwards This is done by forced segmentation fault and looks like this
(dmesg):

pipe00[4678]: segfault at 0 ip 00007f4c8ab77d02 sp 000002ed00000001 error 4

Where %sp encodes line number (32 most significant bits) and error code (32
least significant bits).
Signed-off-by: Stanislav Kinsbursky <skinsbursky@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>

restorer.c

@@ -722,6 +722,9 @@ long restore_task(struct task_restore_core_args *args)
 	sys_sigaction(SIGCHLD, &args->sigchld_act, NULL);
 
 	cr_wait_dec(&args->task_entries->nr_in_progress);
+
+	sys_close(args->logfd);
+
 	cr_wait_while(&args->task_entries->start, CR_STATE_RESTORE_SIGCHLD);
 
 	/*
@@ -742,13 +745,10 @@ long restore_task(struct task_restore_core_args *args)
 
 	ret = sys_munmap(args->task_entries, TASK_ENTRIES_SIZE);
 	if (ret < 0) {
-		write_num_n(__LINE__);
-		write_num_n(ret);
-		goto core_restore_end;
+		ret = ((long)__LINE__ << 32) | -ret;
+		goto core_restore_failed;
 	}
 
-	sys_close(args->logfd);
-
 	/*
 	 * Sigframe stack.
 	 */
@@ -773,4 +773,14 @@ core_restore_end:
 	write_num_n(sys_getpid());
 	sys_exit(-1);
 	return -1;
+
+core_restore_failed:
+	asm volatile(
+		"movq %0, %%rsp				\n"
+		"movq 0, %%rax				\n"
+		"jmp *%%rax				\n"
+		:
+		: "r"(ret)
+		: );
+	return ret;
 }