Re: [PATCH 1/1] driver core: Fix driver_sysfs_remove() order in really_probe()

[Lu Baolu]

Hi Greg,

On 12/29/21 6:04 PM, Greg Kroah-Hartman wrote:
> On Wed, Dec 29, 2021 at 12:51:59PM +0800, Lu Baolu wrote:
> > The driver_sysfs_remove() should always be called after successful
> > driver_sysfs_add(). Otherwise, NULL pointers will be passed to the
> > sysfs_remove_link(), where it is decoded as searching sysfs root.
>
> What null pointer is being sent to sysfs_remove_link()?  For which link?

Oh, my fault. Thank you for pointing this out.

The device and driver sysfs nodes have already been created, so there's
no null pointers. The out-of-order call of driver_sysfs_remove() just
tries to remove some nonexistent nodes under the device and driver sysfs
nodes. It is allowed by the sysfs layer.

> How are you triggering this failure path and how was it tested?

I hacked the a driver to return failure in dma_configure() callback. I
didn't see any failure. But I mistakenly thought that
driver_sysfs_remove() could possibly delete some sysfs entries by
mistake. That's not true. Sorry for the noise.

> > Fixes: 1901fb2604fbc ("Driver core: fix "driver" symlink timing")
> > Cc: stable@xxxxxxxxxxxxxxx

This patch only improves the readability of really_probe() and it does
not fix any bugs. I will remove above tags and resent a version if you
think this improvement is valuable.

> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/base/dd.c | 7 ++++---
> >   1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > index 68ea1f949daa..9eaaff2f556c 100644
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -577,14 +577,14 @@ static int really_probe(struct device *dev, struct device_driver *drv)
> >   	if (dev->bus->dma_configure) {
> >   		ret = dev->bus->dma_configure(dev);
> >   		if (ret)
> > -			goto probe_failed;
> > +			goto pinctrl_bind_failed;
>
> Why not call the notifier chain here?  Did you verify that this change
> still works properly?

The BUS_NOTIFY_DRIVER_NOT_BOUND event is listened in two places in the
tree.

$ git grep BUS_NOTIFY_DRIVER_NOT_BOUND -- :^drivers/base/dd.c :^include
drivers/acpi/acpi_lpss.c:       case BUS_NOTIFY_DRIVER_NOT_BOUND:
drivers/base/power/clock_ops.c: case BUS_NOTIFY_DRIVER_NOT_BOUND:

The usage pattern is setting up something in BUS_NOTIFY_BIND_DRIVER and
doing the cleanup in BUS_NOTIFY_DRIVER_NOT_BOUND or
BUS_NOTIFY_UNBIND_DRIVER. The right order of these events should be

 [failure case]
 - BUS_NOTIFY_BIND_DRIVER: driver is about to be bound
 - BUS_NOTIFY_DRIVER_NOT_BOUND: driver failed to be bound

or

 [successful case]
 - BUS_NOTIFY_BIND_DRIVER: driver is about to be bound
 - BUS_NOTIFY_BOUND_DRIVER: driver bound to device
 - BUS_NOTIFY_UNBIND_DRIVER: driver is about to be unbound
 - BUS_NOTIFY_UNBOUND_DRIVER: driver is unbound from the device

Without above change, when dma_configure() returns failure, the listener 
could get a BUS_NOTIFY_DRIVER_NOT_BOUND without BUS_NOTIFY_BIND_DRIVER.

Please guide me if my understanding is wrong.

> thanks,
>
> greg k-h

Best regards,
baolu