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From: Chanwoo Choi <cw00.choi@samsung.com>
To: Hans de Goede <hdegoede@redhat.com>
Cc: myungjoo.ham@samsung.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Unregistering extcon providers while they are in use leads to kernel crashes
Date: Tue, 27 Dec 2016 14:04:56 +0900	[thread overview]
Message-ID: <5861F678.9010408@samsung.com> (raw)
In-Reply-To: <0c877df4-c5d7-1eae-bff9-469df9651d09@redhat.com>

Hi Hans,

Thanks for your report.
I'll check this problem and try to resolve it.

On 2016년 12월 22일 00:54, 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
> 
> Regards,
> 
> Hans
> 
> 
> 

-- 
Regards,
Chanwoo Choi

      parent reply	other threads:[~2016-12-27  5:05 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
2016-12-27  5:04   ` Chanwoo Choi [this message]

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