audit return code handling for kernel_thread [4/11]

Audit/Cleanup of kernel_thread calls, specifically checking of return codes.
Problems seemed to fall into 3 main categories:

1) callers of kernel_thread were inconsistent about meaning of a zero return code. Some callers considered a zero return code to mean success, others took it to mean failure. a zero return code, while not actually possible in the current implementation, should be considered a success (pid 0 is/should be valid). fixed all callers to treat zero return as success

2) caller of kernel_thread saved return code of kernel_thread for later use without ever checking its value. Callers who did this tended to assume a non-zero return was success, and would often wait for a completion queue to be woken up, implying that an error (negative return code) from kernel_thread could lead to deadlock. Repaired by checking return code at call time, and setting saved return code to zero in the event of an error.

3) callers of kernel_thread never bothered to check the return code at all. This can lead to seemingly unrelated errors later in execution. Fixed by checking return code at call time and printing a warning message on failure.

Regards
Neil

 init/do_mounts_initrd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -57,7 +57,7 @@ static void __init handle_initrd(void)
 
 	current->flags |= PF_NOFREEZE;
 	pid = kernel_thread(do_linuxrc, "/linuxrc", SIGCHLD);
-	if (pid > 0) {
+	if (pid >= 0) {
 		while (pid != sys_wait4(-1, NULL, 0, NULL))
 			yield();
 	}

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