linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hans de Goede <hdegoede@redhat.com>
To: Chanwoo Choi <cw00.choi@samsung.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: Wed, 21 Dec 2016 16:55:13 +0100	[thread overview]
Message-ID: <6f4a329f-d128-a317-513b-1f2aa1690152@redhat.com> (raw)
In-Reply-To: <0c877df4-c5d7-1eae-bff9-469df9651d09@redhat.com>

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

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=6f4a329f-d128-a317-513b-1f2aa1690152@redhat.com \
    --to=hdegoede@redhat.com \
    --cc=cw00.choi@samsung.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=myungjoo.ham@samsung.com \
    --subject='Re: Unregistering extcon providers while they are in use leads to kernel crashes' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).