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SubjectRe: [PATCH] i2c: iproc: fix race between client unreg and isr
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On 7/22/2020 8:51 AM, Ray Jui wrote:
>
> On 7/22/2020 3:41 AM, Wolfram Sang wrote:
>>
>>>> + synchronize_irq(iproc_i2c->irq);
>>>
>>> If one takes a look at the I2C slave ISR routine, there are places where
>>> IRQ can be re-enabled in the ISR itself. What happens after we mask all
>>> slave interrupt and when 'synchronize_irq' is called, which I suppose is
>>> meant to wait for inflight interrupt to finish where there's a chance
>>> the interrupt can be re-enable again? How is one supposed to deal with that?
>>
>> I encountered the same problem with the i2c-rcar driver before I left
>> for my holidays.
>>
>
> 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

Actually, thinking about it more, 1. and 2. here need to be an atomic
operation so it needs to be wrapped by a spin lock/unlock (and it is
safe to do so here before calling synchronize_irq below).

Same applies to the two read-modify-write sequneces to enable some of
the slave interrupts in the 'bcm_iproc_i2c_slave_isr' routine.

>
> 3. synchronize_irq
>
> 4. Set slave to NULL
>
> 5. Erase slave addresses
>
> In the ISR routine, it should always check against 'unreg_slave' before
> enabling any slave interrupt. If 'unreg_slave' is set, no slave
> interrupt should be re-enabled from within the ISR.
>
> I think the above sequence can ensure no further slave interrupt after
> 'synchronize_irq'. I suggested using an atomic variable instead of
> variable + spinlock due to the way how sync irq works, i.e., "If you use
> this function while holding a resource the IRQ handler may need you will
> deadlock.".
>
> Thanks,
>
> Ray
>
>>>> + iproc_i2c->slave = NULL;
>>>> +
>>>> /* Erase the slave address programmed */
>>>> tmp = iproc_i2c_rd_reg(iproc_i2c, S_CFG_SMBUS_ADDR_OFFSET);
>>>> tmp &= ~BIT(S_CFG_EN_NIC_SMB_ADDR3_SHIFT);
>>>>

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