Re: [PATCH] tpm/tpm_tis: Fix variable reset during IRQ probing

[Tianjia Zhang <tianjia.zhang@linux.alibaba.com>]

On 1/14/21 10:51 AM, Jarkko Sakkinen wrote:
> On Wed, Jan 13, 2021 at 08:00:21PM +0800, Tianjia Zhang wrote:
>> In tpm_tis_core_init(), tpm2_probe() will be called first, this
>> function will eventually call tpm_tis_send(), and then
>> tpm_tis_probe_irq_single() will detect whether the interrupt is
>> normal, mainly the installation interrupted, set `priv->irq_tested`
>> to false. The logic will eventually be executed to tpm_tis_send()
>> to trigger an interrupt.
>>
>> There is currently such a scenario, which will cause the IRQ probe
>> code to never be executed, so that the TPM device is in polling
>> mode: after setting irq_tested to false, an interrupt occurs
>> between entering the ttpm_tis_send() function, and the interrupt
>> will be first set irq_tested to true will cause the IRQ probe code
>> to never be executed.
> 
> Can you describe the scenario more detail?
> 

The problematic scenario we encountered is like this. The following 
figure shows the execution flow of tpm_tis_core_init(). An interrupt 
occurred before the IRQ probe. This interrupt was caused by 
tpm2_probe(), but it was triggered before the IRQ probe was executed, 
and the interrupt handler would set irq_tested to true, so the IRQ probe 
code can never execute, that is, the code marked 2 in the figure will 
never happen.

                                          IRQ
   tpm_tis_core_init()

     tpm2_probe()

       tpm_tis_send()           -----------+
                                           |
     tpm_tis_probe_irq_single()            |
                                           |
       devm_request_irq()                  | 1
       priv->irq_tested = false            |
       tpm_tis_gen_interrupt()             |
                                           |
         tpm_tis_send()                    |
                         irq_tested = true |
                        <------------------+
           if (priv->irq_tested)
             return tpm_tis_send_main()

           /* probe IRQ */
           tpm_tis_send_main()     --------+
                                           | 2
           chip->flags |= FLAG_IRQ <-------+
           priv->irq_tested = true

Best regards,
Tianjia