kobject: don't use WARN for registration failures

BugLink: http://bugs.launchpad.net/bugs/1768825

commit 3e14c6ab upstream.

This WARNING proved to be noisy. The function still returns an error
and callers should handle it. That's how most of kernel code works.
Downgrade the WARNING to pr_err() and leave WARNINGs for kernel bugs.
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Reported-by: syzbot+209c0f67f99fec8eb14b@syzkaller.appspotmail.com
Reported-by: syzbot+7fb6d9525a4528104e05@syzkaller.appspotmail.com
Reported-by: syzbot+2e63711063e2d8f9ea27@syzkaller.appspotmail.com
Reported-by: syzbot+de73361ee4971b6e6f75@syzkaller.appspotmail.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

lib/kobject.c

@@ -234,12 +234,10 @@ static int kobject_add_internal(struct kobject *kobj)
 
 		/* be noisy on error issues */
 		if (error == -EEXIST)
-			WARN(1, "%s failed for %s with "
-			     "-EEXIST, don't try to register things with "
-			     "the same name in the same directory.\n",
+			pr_err("%s failed for %s with -EEXIST, don't try to register things with the same name in the same directory.\n",
 			       __func__, kobject_name(kobj));
 		else
-			WARN(1, "%s failed for %s (error: %d parent: %s)\n",
+			pr_err("%s failed for %s (error: %d parent: %s)\n",
 			       __func__, kobject_name(kobj), error,
 			       parent ? kobject_name(parent) : "'none'");
 	} else