From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hellhawk.shadowen.org (hellhawk.shadowen.org [80.68.90.175]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 7B51EDDFAC for ; Fri, 4 May 2007 22:19:58 +1000 (EST) From: Andy Whitcroft Sender: Andy Whitcroft To: gregkh@suse.de,paulus@samba.org Subject: [PATCH] Re: 2.6.21-rc7-mm2 -- hvsi console driver registration failure References: <20070425225716.8e9b28ca.akpm@linux-foundation.org> Message-ID: <4fe4528cb20beb569a8f2ac817c776e5@pinky> Date: Fri, 04 May 2007 12:38:58 +0100 Cc: Andrew Morton , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Trying to get 2.6.21-rc7-mm2 to boot on large PPC64 seems to be a bit of a challenge. We have been seeing panics on boot from the hvsi driver: Couldn't register hvsi console driver Tracking this back, this seems to come from hvsi driver trying to register itself via tty_register_driver() with a zero units. The failure is triggered by a change in semantics for kmalloc() between SLAB and SLUB; kmalloc(0) now returns NULL rather than an allocation at the smallest size. Looking at the code in question even when the allocation succeeds we will not actually use the memory when device->num is zero. It is not clear to me if this is a bug in the hvsi driver in that it should specify some units. It seems we will try and reserve zero devices in this case, which seems pointless. I have tested with the patch below which seems safe to me and stops the errors and even seems to make the console work. But perhaps someone with more driver fu, could verify if driver->num of zero has any meaning and kick this to the hvsi people if not. -apw === 8< === tty_register_driver: only allocate tty instances when defined If device->num is zero we attempt to kmalloc() zero bytes. When SLUB is enabled this returns a null pointer and take that as an allocation failure and fail the device register. Check for no devices and avoid the allocation. Signed-off-by: Andy Whitcroft --- diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index 959a616..71c4579 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -3724,7 +3724,7 @@ int tty_register_driver(struct tty_driver *driver) if (driver->flags & TTY_DRIVER_INSTALLED) return 0; - if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM)) { + if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM) && driver->num) { p = kmalloc(driver->num * 3 * sizeof(void *), GFP_KERNEL); if (!p) return -ENOMEM;