Hi Andrey, On Mon, Apr 09, 2018 at 09:00:52AM -0700, Andrey Smirnov wrote: > On Tue, Apr 3, 2018 at 12:04 AM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote: > > On Mon, Mar 26, 2018 at 06:09:15AM -0700, Andrey Smirnov wrote: > >> In order to allow 'serdev' devices to prevent parent console device > >> removal and correspondign memory deallocation add code to all serial > >> driver to check result of console_unregister() and bail out early if > >> it is unsuccessful. > >> > >> One example of a use-case for this would be a reset handler relying on > >> a serdev device for transport. Without this patch underlying console > >> device would be removed and de-allocated before reset handler is even > >> run thus leading to unpredictable behaviour and crashes. > > > > Can't we make this sure at driver core level? > > I need to be able to prevent serial driver's "remove" function from > ever executing to prevent any de-initialization/memory freeing from > happening. The simplest way to solve this in driver core that comes to > my mind is implementing simple reference counting API that children > could use to force driver core to bail out on removing parents if they > are still in use. Does that sound like a reasonable idea? > > > So if a device decides not > > to return -EBUSY in the remove callback then the parent devices won't be > > removed? > > Remove callback currently returns void, we could change it to return > int and use it to implement a sort of implicit refcounting, but doing > so would result in quite a bit of code churn since all of the current > drivers would have to be converted to return int in their .remove > callbacks. Would you rather I do this or explicit refcounting? Normally it helps looking at the Linux kernel to see how a problem is solved there. Not so this time it seems. Linux distinguishes between "remove" and "shutdown". "shutdown" is what we want during barebox shutdown. I found a Linux driver that is similar to your situation: It registers a restart_handler while being a i2c device itself. There seems to be no way to prevent a device from being shutdown, it's only that the i2c bus drivers simply do not implement it. Where do we go from here? I think reference counting is a bit over the top. At the moment I would opt for a *very* simple solution: Let's drop the call to console_unregister() and the freeing of resources entirely as it gives us nothing. The only console driver I can see where removing is valid is drivers/usb/gadget/u_serial.c and you won't use this for restarting a SoC ;) Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
