ping // [PATCH] mtd:cfi_cmdset_0002: fix atomic sleep bug when CONFIG_MTD_XIP=y

[Xiaoming Ni]

On 2020/12/8 2:59, Vignesh Raghavendra wrote:
> Hi Xiaoming,
> 
> On 12/7/20 4:23 PM, Miquel Raynal wrote:
>> Hi Xiaoming,
>>
>> Xiaoming Ni <nixiaoming at huawei.com> wrote on Mon, 7 Dec 2020 18:48:33
>> +0800:
>>
>>> ping
>>>
>>> On 2020/11/27 21:07, Xiaoming Ni wrote:
>>>> When CONFIG_MTD_XIP=y, local_irq_disable() is called in xip_disable().
>>>> To avoid sleep in interrupt context, we need to call local_irq_enable()
>>>> before schedule().
>>>>
>>>> The problem call stack is as follows:
>>>> bug1:
>>>> 	do_write_oneword_retry()
>>>> 		xip_disable()
>>>> 			local_irq_disable()
>>>> 		do_write_oneword_once()
>>>> 			schedule()
>>>> bug2:
>>>> 	do_write_buffer()
>>>> 		xip_disable()
>>>> 			local_irq_disable()
>>>> 		do_write_buffer_wait()
>>>> 			schedule()
>>>> bug3:
>>>> 	do_erase_chip()
>>>> 		xip_disable()
>>>> 			local_irq_disable()
>>>> 		schedule()
>>>> bug4:
>>>> 	do_erase_oneblock()
>>>> 		xip_disable()
>>>> 			local_irq_disable()
>>>> 		schedule()
>>>>
>>>> Fixes: 02b15e343aee ("[MTD] XIP for AMD CFI flash.")
>>>> Cc: stable at vger.kernel.org # v2.6.13
>>>> Signed-off-by: Xiaoming Ni <nixiaoming at huawei.com>
>>>> ---
>>>>    drivers/mtd/chips/cfi_cmdset_0002.c | 16 ++++++++++++++++
>>>>    1 file changed, 16 insertions(+)
>>>>
>>>> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c
>>>> index a1f3e1031c3d..12c3776f093a 100644
>>>> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
>>>> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
>>>> @@ -1682,7 +1682,11 @@ static int __xipram do_write_oneword_once(struct map_info *map,
>>>>    			set_current_state(TASK_UNINTERRUPTIBLE);
>>>>    			add_wait_queue(&chip->wq, &wait);
>>>>    			mutex_unlock(&chip->mutex);
>>>> +			if (IS_ENABLED(CONFIG_MTD_XIP))
>>>> +				local_irq_enable();
>>>>    			schedule();
>>>> +			if (IS_ENABLED(CONFIG_MTD_XIP))
>>>> +				local_irq_disable();
>>
>> The fix really seems strange to me. I will let Vignesh decide but I
>> think we should consider updating/fixing xip_disable instead.
> 
> Agree with Miquel. Have you done any testing
> or is this purely based on code inspection?
> 
I don't have the corresponding device test environment.
I found the problem through code review.


> What about comment before xip_disable() function:
> 
> /*
>   * No interrupt what so ever can be serviced while the flash isn't in array
>   * mode.  This is ensured by the xip_disable() and xip_enable() functions
>   * enclosing any code path where the flash is known not to be in array mode.
>   * And within a XIP disabled code path, only functions marked with __xipram
>   * may be called and nothing else (it's a good thing to inspect generated
>   * assembly to make sure inline functions were actually inlined and that gcc
>   * didn't emit calls to its own support functions). Also configuring MTD CFI
>   * support to a single buswidth and a single interleave is also recommended.
>   */
> 
> So, I don't think the fix is as simple as this patch.
>
+xip_enable();
  schedule();
+xip_disable();

Do I need to change it to this?



> Regards
> Vignesh
> .
> 

Thanks
Xiaoming Ni