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

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Date:   Mon, 27 Jul 2020 13:43:40 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Wolfram Sang <wsa@...nel.org>
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 7/27/2020 1:26 PM, Wolfram Sang wrote:
> 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!
> 

Sure. I suggest Dhananjay gives the sequence you proposed here a try
(with delay added during the testing to widen the window to cover corner
cases). If it works, we can just go with your proposed sequence here.

Thanks!

Ray