Comment 9 for bug 1469218

Some static code analysis:

1), looks not possbile in scsi request submit path
- preempt is disabled for arm64 vivid
- the timer is always added just before submitting to hardware
- once it can't be submitted to hardware, the timer is disabled

2), another possibility is in ata's completion path
- block request is always completed in softirq(scsi_done()->blk_complete_request())
- the softirq may be run from another CPU, which is triggered by IPI
- but one atomic complete flag is used to monitor the request completion status
(blk_mark_rq_complete()), so looks the timeout can't be caused by softirq delay schedule.