linux-kernel - Re: [PATCH] i2c: iproc: fix race between client unreg and isr

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Date:   Mon, 27 Jul 2020 10:02:09 +0530
From:   Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
To:     Wolfram Sang <wsa@...nel.org>
Cc:     Ray Jui <ray.jui@...adcom.com>,
        Dhananjay Phadke <dphadke@...ux.microsoft.com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ray Jui <rjui@...adcom.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH] i2c: iproc: fix race between client unreg and isr

On Sat, Jul 25, 2020 at 3:48 PM Wolfram Sang <wsa@...nel.org> wrote:
>
>
> > I think the following sequence needs to be implemented to make this
> > safe, i.e., after 'synchronize_irq', no further slave interrupt will be
> > fired.
> >
> > In 'bcm_iproc_i2c_unreg_slave':
> >
> > 1. Set an atomic variable 'unreg_slave' (I'm bad in names so please come
> > up with a better name than this)
> >
> > 2. Disable all slave interrupts
> >
> > 3. synchronize_irq
> >
> > 4. Set slave to NULL
> >
> > 5. Erase slave addresses
>
> What about this in unreg_slave?
>
> 1. disable_irq()
>         This includes synchronize_irq() and avoids the race. Because irq
>         will be masked at interrupt controller level, interrupts coming
>         in at the I2C IP core level should still be pending once we
>         reenable the irq.
>
> 2. disable all slave interrupts
>
> 3. enable_irq()
>
> 4. clean up the rest (pointer, address)
>
> Or am I overlooking something?

This sequence will take care of all cases.

@Dhananjay Phadke is it possible to verify this from your side once.

Best regards,
Raaygonda