do_coredump: fix the "ispipe" error check

do_coredump() assumes that if format_corename() fails it should return
-ENOMEM.  This is not true, for example cn_print_exe_file() can propagate
the error from d_path.  Even if it was true, this is too fragile.  Change
the code to check "ispipe < 0".
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -2133,16 +2133,16 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 
 	ispipe = format_corename(&cn, signr);
 
-	if (ispipe == -ENOMEM) {
+ 	if (ispipe) {
+		int dump_count;
+		char **helper_argv;
+
+		if (ispipe < 0) {
 			printk(KERN_WARNING "format_corename failed\n");
 			printk(KERN_WARNING "Aborting core\n");
 			goto fail_corename;
 		}
 
- 	if (ispipe) {
-		int dump_count;
-		char **helper_argv;
-
 		if (cprm.limit == 1) {
 			/*
 			 * Normally core limits are irrelevant to pipes, since