I am getting kernel panic (NULL pointer dereference) on boot, with kernel
compiled with CONFIG_SND_MPU401_UART=y, on machine which does not have
this piece of hardware.
I have traced the problem down to
sound/drivers/mpu401/mpu401.c:snd_mpu401_probe() returning EINVAL, when
either port or IRQ parameters are not specified.
In such case, the drivers/base/bus.c:bus_attach_device() does not perform
klist_add_tail() call, but rather sets dev->is_registered to 0. This flag
is however not checked by the driver, so later on, when
alsa_card_mpu401_init() is called and platform_device_register_simple()
fails, the following callchain happens, causing NULL pointer dereference:
alsa_card_mpu401_init() -> platform_device_unregister() ->
platform_device_del() -> device_del() -> bus_remove_device() ->
klist_del() -> BOOM (the entry was not added to klist in
bus_attach_device()).
Proper solution is returning ENODEV from the ->probe() routine, which will
be correctly handled then by the rest of the device-driver attaching
subsystem (namely the retval check in bus_attach_device()). The following
patch fixes the problem, please apply.
Patch against current Linus' git tree.
Signed-off-by: Jiri Kosina <jikos@xxxxxxxx>
--- a/sound/drivers/mpu401/mpu401.c
+++ b/sound/drivers/mpu401/mpu401.c
@@ -104,11 +104,11 @@ static int __devinit snd_mpu401_probe(st
if (port[dev] == SNDRV_AUTO_PORT) {
snd_printk(KERN_ERR "specify port\n");
- return -EINVAL;
+ return -ENODEV;
}
if (irq[dev] == SNDRV_AUTO_IRQ) {
snd_printk(KERN_ERR "specify or disable IRQ\n");
- return -EINVAL;
+ return -ENODEV;
}
err = snd_mpu401_create(dev, &card);
if (err < 0)
--
Jiri Kosina
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