[PATCH v2 01/10] drivers: PL011: avoid potential unregister_driver call

[Russell King - ARM Linux]

On Wed, Apr 08, 2015 at 04:39:03PM +0100, Andre Przywara wrote:
> Hi Russell,
> 
> On 12/03/15 10:42, Russell King - ARM Linux wrote:
> > On Wed, Mar 04, 2015 at 05:59:45PM +0000, Andre Przywara wrote:
> >> Although we care about not unregistering the driver if there are
> >> still ports connected during the .remove callback, we do miss this
> >> check in the pl011_probe function. So if the current port allocation
> >> fails, but there are other ports already registered, we will kill
> >> those.
> >> So factor out the port removal into a separate function and use that
> >> in the probe function, too.
> >>
> >> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
> >> ---
> >>  drivers/tty/serial/amba-pl011.c |   38 +++++++++++++++++++++-----------------
> >>  1 file changed, 21 insertions(+), 17 deletions(-)
> >>
> >> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> >> index 92783fc..961f9b0 100644
> >> --- a/drivers/tty/serial/amba-pl011.c
> >> +++ b/drivers/tty/serial/amba-pl011.c
> >> @@ -2235,6 +2235,24 @@ static int pl011_probe_dt_alias(int index, struct device *dev)
> >>  	return ret;
> >>  }
> >>  
> >> +/* unregisters the driver also if no more ports are left */
> >> +static void pl011_unregister_port(struct uart_amba_port *uap)
> >> +{
> >> +	int i;
> >> +	bool busy = false;
> >> +
> >> +	for (i = 0; i < ARRAY_SIZE(amba_ports); i++) {
> >> +		if (amba_ports[i] == uap)
> >> +			amba_ports[i] = NULL;
> >> +		else if (amba_ports[i])
> >> +			busy = true;
> >> +	}
> >> +	pl011_dma_remove(uap);
> >> +	if (!busy)
> >> +		uart_unregister_driver(&amba_reg);
> >> +}
> > 
> > This is still racy, as I pointed out at the time this crap was dreamt
> > up.
> > 
> > There is _no_ locking between an individual driver's ->probe or ->remove
> > functions being called concurrently for different devices.  The only
> > locking which the driver model guarantees is that a single struct device
> > can only be probed by one driver at a time.
> > 
> > Multiple struct device's can be in-progress of ->probe or ->remove
> > simultaneously.
> 
> OK, I see.
> 
> > However, this isn't your bug to solve... it's those who were proponents
> > of this crap approach.
> 
> Does that mean you want me to drop this patch? It isn't strictly
> necessary for my series. So do you want to postpone a fix until later
> when there is a real solution (tm) for this issue or shall I include
> this still in my series for fixing at least half of the issue?

Sorry, it's been way too long since my mail was sent, I've lost all
context about it.

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