On Mon, Jun 12, 2023 at 11:44:00AM +0200, Peter Zijlstra wrote:
> On Mon, Jun 12, 2023 at 11:07:59AM +0200, Peter Zijlstra wrote:
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > ---
> > kernel/events/core.c | 65 ++++++++++++++++++++++++---------------------------
> > 1 file changed, 31 insertions(+), 34 deletions(-)
> >
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -11285,49 +11285,46 @@ static void pmu_dev_release(struct devic
> >
> > static int pmu_dev_alloc(struct pmu *pmu)
> > {
> > + int ret;
> >
> > + struct device *dev __free(put_device) =
> > + kzalloc(sizeof(struct device), GFP_KERNEL);
> > + if (!dev)
> > + return -ENOMEM;
> >
> > + dev->groups = pmu->attr_groups;
> > + device_initialize(dev);
> >
> > + dev_set_drvdata(dev, pmu);
> > + dev->bus = &pmu_bus;
> > + dev->release = pmu_dev_release;
> >
> > + ret = dev_set_name(dev, "%s", pmu->name);
> > if (ret)
> > + return ret;
> >
> > + ret = device_add(dev);
> > if (ret)
> > + return ret;
> >
> > + struct device *del __free(device_del) = dev;
>
> Greg, I'm not much familiar with the whole device model, but it seems
> unfortunate to me that one has to call device_del() explicitly if we
> already have a put_device() queued.
>
> Is there a saner way to write this?
Ok, the "problem" here is that you have decided to do the "complex" way
to initialize a struct device. And as such, you have to do more
housekeeping than if you were to just use the simple interface.
The rule is, after you call device_initialize() you HAVE to call
put_device() on the pointer if something goes wrong and you want to
clean up properly. Unless you have called device_add(), and at that
point in time, then you HAVE to call device_del() if the device_add()
call succeeded. If the device_add() call failed, then you HAVE to call
put_device().
Yeah, it's a pain, but you are trying to hand-roll code that is not a
"normal" path for a struct device, sorry.
I don't know if you really can encode all of that crazy logic in the
cleanup api, UNLESS you can "switch" the cleanup function at a point in
time (i.e. after device_add() is successful). Is that possible?
Anyway, let me see about just cleaning up this code in general, I don't
think you need the complex interface here for a tiny struct device at
all, which would make this specific instance moot :)
Also, nit, you are racing with userspace by attempting to add new device
files _AFTER_ the device is registered with the driver core, this whole
thing can be made more simpler I hope, give me a bit...
thanks
greg k-h
