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: Re: Unregistering extcon providers while they are in use leads to kernel crashes Date: Wed, 21 Dec 2016 16:55:13 +0100 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> Hi, On 21-12-16 16:54, Hans de Goede wrote: > 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 p.s. In case it was not clear, I noticed this, but I don't have the time to fix it, which is why I wrote the above plan with the hope that someone can use it as a base to actual fix this. Regards, Hans
next prev parent reply other threads:[~2016-12-21 15:55 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 2016-12-21 15:55 ` Hans de Goede [this message] 2016-12-27 5:04 ` Chanwoo Choi
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