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

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Message-ID: <Y7QVh8/LPQ7H8ehp@shell.armlinux.org.uk>
Date:   Tue, 3 Jan 2023 11:46:15 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
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 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 fundamental principles of kernel programming: do not publish data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.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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