Messages in this thread | | | From | Andy Shevchenko <> | Date | Mon, 1 Jun 2020 17:08:40 +0300 | Subject | Re: [PATCH 0/6] leds: fix broken devres usage |
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On Mon, Jun 1, 2020 at 5:01 PM Johan Hovold <johan@kernel.org> wrote: > > On Mon, Jun 01, 2020 at 04:51:01PM +0300, Andy Shevchenko wrote: > > On Mon, Jun 1, 2020 at 4:42 PM Johan Hovold <johan@kernel.org> wrote: > > > > > > Several MFD child drivers register their class devices directly under > > > the parent device (about half of the MFD LED drivers do so). > > > > > > This means you cannot blindly do devres conversions so that > > > deregistration ends up being tied to the parent device, something which > > > leads to use-after-free on driver unbind when the class device is > > > released while still being registered (and, for example, oopses on later > > > parent MFD driver unbind or LED class callbacks, or resource leaks and > > > name clashes on child driver reload). > > > > Shouldn't MFD take reference count for their children? > > That's not the issue here. The child driver is allocating memory for the > class device (for example using devres), and that will end up being > freed on unbind while said device is still registered. The child driver > may then even be unloaded. No extra reference can fix this.
Okay, I didn't still get how dropping devres will help here.
Say, we have
->probe() { return devm_foo_register(); }
and no ->remove()
vs.
->probe() { return foo_register(); }
->remove() { foo_unregister(); }
So, basically what you seem to workaround is that ->remove() is not getting called?
-- With Best Regards, Andy Shevchenko
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