Hello Thomas, Thanks for the feedback. On 4/25/22 10:27, Thomas Zimmermann wrote: > Hi > > Am 20.04.22 um 10:53 schrieb Javier Martinez Canillas: >> Drivers that want to remove registered conflicting framebuffers prior to >> register their own framebuffer, calls remove_conflicting_framebuffers(). >> >> This function takes the registration_lock mutex, to prevent a races when >> drivers register framebuffer devices. But if a conflicting framebuffer >> device is found, the underlaying platform device is unregistered and this >> will lead to the platform driver .remove callback to be called, which in >> turn will call to the unregister_framebuffer() that takes the same lock. >> >> To prevent this, a struct fb_info.forced_out field was used as indication >> to unregister_framebuffer() whether the mutex has to be grabbed or not. >> >> A cleaner solution is to drop the lock before platform_device_unregister() >> so unregister_framebuffer() can take it when called from the fbdev driver, >> and just grab the lock again after the device has been registered and do >> a removal loop restart. > > I don't see how this patch improves the situation. So far, > do_remove_conflicting_framebuffers() had no business in maintaining > locks. And now it's doing this in in a goto-loop where it keeps > getting/dropping locks. That's asking for bugs IMHO. > It's true that do_remove_conflicting_framebuffers() gets more complicated with all the locks release/re-acquire but OTOH unregister_framebuffer() doesn't do conditionally locking, and more importantly the drivers .remove callback isn't called with the lock held, which IMHO is also quite fragile. -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat
