linux-kernel - Re: [PATCH] regulator: core: fix race condition in regulator

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Date:	Thu, 8 Jan 2015 12:58:03 -0000
From:	ashayj@...eaurora.org
To:	"Mark Brown" <broonie@...nel.org>
Cc:	"Ashay Jaiswal" <ashayj@...eaurora.org>,
	"Liam Girdwood" <lgirdwood@...il.com>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	"Anirudh Ghayal" <aghayal@...eaurora.org>,
	"David Collins" <collinsd@...eaurora.org>
Subject: Re: [PATCH] regulator: core: fix race condition in regulator_put()

Thanks Mark for your review comments.

> On Wed, Jan 07, 2015 at 07:21:23PM +0530, Ashay Jaiswal wrote:
>
>> The regulator framework maintains a list of consumer regulators
>> for a regulator device and protects it from concurrent access
>> using the regulator device's mutex lock.
>
>> In the case of regulator_put() the consumer is removed without
>> holding the regulator device's mutex, resulting in a race condition
>> between any regulator operation which traverses the consumer list
>> and regulator_put() which releases the consumer regulator.
>> Fix this race condition by holding the regulator device's mutex while
>> removing and releasing the consumer regulator.
>
> This is a good spot thanks but I think your analysis here is missing a
> bit - it's not just the list manipulation that affects the rdev, it's
> also the reference count in the rdev and the exclusive flag.  Indeed
> some of this issue applies on the _get() side too, while we do add the
> regulator to the list under the rdev mutex we don't have the mutex when
> we update the reference count meaning that we've got a potential issue
> with that.  That *is* kind of separate though so could be dealt with in
> a separate patch.
>

I have updated the commit message as per your suggestion.
I will try to fix the regulator_get path.

> The lock region also seems too wide, the lock is only needed for the
> operations that affect the rdev not for the operations only on the
> object being freed - holding the lock for too long means impacting other
> users and some of the cleanup is potentially expensive.  The comment at
> the top of the function needs updating too, it currently says that the
> lock is held in the caller but this applies only to the
> regulator_list_mutex.
>
Yes I too agree with your suggestion, updated the lock region to protect
only rdev parameters.
Also updated the comment on top of the _regulator_put function to reflect
regulator_list_mutex lock is held by caller.

I will upload next version of patch incorporating all the review comments.

Ashay Jaiswal


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