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SubjectRe: [PATCH v2 2/2] arm: perf: Mark as non-removable
Date
Hi,

On Thursday 22 December 2016 22:48:32, Mark Rutland wrote:
> On Wed, Dec 21, 2016 at 04:03:40PM +0100, Alexander Stein wrote:
> > This driver can only built into the kernel. So disallow driver bind/unbind
> > and also prevent a kernel error in case DEBUG_TEST_DRIVER_REMOVE is
> > enabled.
> >
> > Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
> > ---
> >
> > arch/arm/kernel/perf_event_v7.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm/kernel/perf_event_v7.c
> > b/arch/arm/kernel/perf_event_v7.c index b942349..795e373 100644
> > --- a/arch/arm/kernel/perf_event_v7.c
> > +++ b/arch/arm/kernel/perf_event_v7.c
> > @@ -2029,6 +2029,7 @@ static int armv7_pmu_device_probe(struct
> > platform_device *pdev)>
> > static struct platform_driver armv7_pmu_driver = {
> >
> > .driver = {
> >
> > .name = "armv7-pmu",
> >
> > + .suppress_bind_attrs = true,
> >
> > .of_match_table = armv7_pmu_of_device_ids,
> >
> > },
>
> While this patch looks correct, the other perf_event_* drivers (e.g. those
> under arch/arm/) will need similar treatment.

Yep, but this is the only one I can actually test.

> More generally, updating each and every driver in this manner seems like a
> scattergun approach that is tiresome and error prone.
>
> IMO, it would be vastly better for a higher layer to enforce that we don't
> attempt to unbind drivers where the driver does not have a remove callback,
> as is the case here (and I suspect most over cases where
> DEBUG_TEST_DRIVER_REMOVE is blowing up).

You mean something like this?
> diff --git a/drivers/base/driver.c b/drivers/base/driver.c
> index 4eabfe2..3b6c1a2d 100644
> --- a/drivers/base/driver.c
> +++ b/drivers/base/driver.c
> @@ -158,6 +158,9 @@ int driver_register(struct device_driver *drv)
>
> printk(KERN_WARNING "Driver '%s' needs updating - please use
> "
>
> "bus_type methods\n", drv->name);
>
> + if (!drv->remove)
> + drv->suppress_bind_attrs = true;
> +
>
> other = driver_find(drv->name, drv->bus);
> if (other) {
>
> printk(KERN_ERR "Error: Driver '%s' is already registered, "

> Is there any reason that can't be enforced at the bus layer, say?

I'm not sure if the change above works with remove functions set in struct
bus_type too.
But on the other hand this would hide errors in drivers which are actually
removable but do not cleanup properly which DEBUG_TEST_DRIVER_REMOVE tries to
detect. By setting .suppress_bind_attrs = true explicitely you state "This
driver cannot be removed!", so the remove callback is not missing by accident.

Best regards,
Alexander

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