Re: [PATCH] ohci-hcd: Fix race condition caused by ohci_urb_enqueue() and io_watchdog_func()

[Yoshida, Shigeru]

Hi Alan,

On Thu, 1 Feb 2018 10:33:33 -0500, Alan Stern wrote:
>> I think we must choose an invalid frame number for the special
>> sentinel value, but I'm not sure which value is adequate for it.
>> Is 0xffffff00 an invalid frame number, otherwise how about simply
>> -1(0xffffffff)?
> 
> Well, the frame_no register is 32 bits wide, but only the 16 low-order 
> bits are meaningful.  ohci_frame_no() strips off the high-order 16 
> bits, so any value with one of those bits set would be acceptable.  
> (Besides, valid frame numbers only go up to 2047.)
> 
> I chose 0xffffff00 because PCI reads from a non-working device 
> generally get a value with all the bits set.  But since the upper 16 
> bits are masked away anyhow, it doesn't matter.  -1u would be fine.

Thanks, I choose 0xffffff00 as you suggested, and will prepare v2 patch.

Thanks,
Shigeru