linux-kernel - Re: [PATCH] nvmem: fix registration vs use race

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Message-ID: <a1143ca2-9460-f156-58a7-66072034559c@linaro.org>
Date:   Tue, 3 Jan 2023 12:42:49 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Hector Martin <marcan@...can.st>
Subject: Re: [PATCH] nvmem: fix registration vs use race



On 03/01/2023 11:46, Russell King (Oracle) wrote:
> On Tue, Jan 03, 2023 at 11:30:36AM +0000, Srinivas Kandagatla wrote:
>>
>>
>> On 03/01/2023 09:42, Russell King (Oracle) wrote:
>>> The i.MX6 CPU frequency driver sometimes fails to register at boot time
>>> due to nvmem_cell_read_u32() sporadically returning -ENOENT.
>>>
>>> This happens because there is a window where __nvmem_device_get() in
>>> of_nvmem_cell_get() is able to return the nvmem device, but as cells
>>> have been setup, nvmem_find_cell_entry_by_node() returns NULL.
>>>
>>> The occurs because the nvmem core registration code violates one of the
>>> fundamental principles of kernel programming: do not publish data
>>> structures before their setup is complete.
>>>
>>> Fix this by making nvmem core code conform with this principle.
>>>
>> how about a Fixes tag and Cc stable?
> 
> Which commit do you suggest? This error goes all the way back to the
> inception of nvmem, commit
> 
> eace75cfdcf7 ("nvmem: Add a simple NVMEM framework for nvmem providers")
> 
> but clearly its going to be a lot of effort to backport it all the
> way due to all the changes.

I understand the backport issue, On the other hand as this a real issue 
backporting to atleast stable kernels would be worth.

--srini
>