From: Hans de Goede <email@example.com> To: Chanwoo Choi <firstname.lastname@example.org> Cc: email@example.com, Linux Kernel Mailing List <firstname.lastname@example.org> Subject: Unregistering extcon providers while they are in use leads to kernel crashes Date: Wed, 21 Dec 2016 16:54:27 +0100 [thread overview] Message-ID: <email@example.com> (raw) Hi, With the recent extcon work I've been doing I noticed that if I want to rmmod and then insmod say extcon_axp288 I can do so without problems even if axp288_charger is holding a reference to the extcon device returned by extcon_get_extcon_dev. The problem is that extcon_get_extcon_dev simply looks up the extcon-device in the list of current registered extcon-s and then returns a pointer to it, without any reference counting. The rmmod scenario can be fixed by doing a module_get from extcon_get_extcon_dev, but that still leaves the same problem when root manually unbinds the driver through sysfs. A possible way fix this would be: 1) Make all extcon providers use devm_extcon_dev_allocate and document using this to allocate an extcon_dev mandatory 2) Add a refcount to struct extcon_dev and introduce extcon_dev_get and extcon_dev_put helpers which modify the refcount and only free the memory on the final put (and make the evm_extcon_dev_allocate cleanup function call extcon_dev_put) 3) On extcon_dev_unregister set a flag in the extcon_dev that it has been free-ed, make all extcon consumer functions which take an extcon_dev (extcon_get_state, extcon_register_notifier, etc.) check this flag and return -ENODEV when the extcon has been unregistered 4) Make extcon_get_extcon_dev call extcon_dev_get on the returned edev before returning it From here on we've fixed the crash, but we now leak the extcon_dev when the consumer gets unbound. 5) Add a devm_extcon_get_extcon_dev which calls extcon_dev_put as the devm cleanup function 6) Convert all extcon consumers to use devm_extcon_get_extcon_dev Regards, Hans
next reply other threads:[~2016-12-21 15:54 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <CGME20161221155432epcas2p4c811f99cc0c82bc1f29cb74f29228300@epcas2p4.samsung.com> 2016-12-21 15:54 ` Hans de Goede [this message] 2016-12-21 15:55 ` Hans de Goede 2016-12-27 5:04 ` Chanwoo Choi
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