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

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Message-ID: <20200727202657.GA18997@ninjato>
Date:   Mon, 27 Jul 2020 22:26:57 +0200
From:   Wolfram Sang <wsa@...nel.org>
To:     Ray Jui <ray.jui@...adcom.com>
Cc:     Dhananjay Phadke <dphadke@...ux.microsoft.com>,
        Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ray Jui <rjui@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH] i2c: iproc: fix race between client unreg and isr

On Mon, Jul 27, 2020 at 08:13:46PM +0200, Wolfram Sang wrote:
> 
> > Can you confirm that even if we have irq pending at the i2c IP core
> > level, as long as we execute Step 2. below (to disable/mask all slave
> > interrupts), after 'enable_irq' is called, we still will not receive any
> > further i2c slave interrupt?
> 
> This is HW dependant. From my tests with Renesas HW, this is not the
> case. But the actual error case was impossible to trigger for me, so
> far. I might try again later. But even in the worst case, I would only
> get a "spurious interrupt" and not an NULL-ptr OOPS.

Let me explain how I verified this:

0) add a debug print whenever the slave irq part is called

1) Put a 2 second delay after disable_irq() and before clearing
interrupt enable register

2) unbind the slave driver in the background, triggering the 2s delay

3) during the delay, try to read from the to-be-unbound slave in the
   foreground

4) ensure there is no prinout from the slave irq

Worked fine for me with the Renesas R-Car I2C IP interface. As mentioned
before, I couldn't trigger a bad case with my setup. So, I hope this new
fix will work for Rayagonda's test case, too!


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