Hi Bart
On 04/20/2018 12:43 AM, Bart Van Assche wrote:
> Use the deadline instead of the request generation to detect whether
> or not a request timer fired after reinitialization of a request
Maybe use deadline to do this is not suitable.
Let's think of the following scenario.
T1/T2 times in nano seconds
J1/J2 times in jiffies
rq is started at T1,J1
blk_mq_timeout_work
-> blk_mq_check_expired
-> save rq->__deadline (J1 + MQ_RQ_IN_FLIGHT)
rq is completed and freed
rq is allocated and started again
on T2
rq->__deadline = J2 +
MQ_RQ_IN_FLIGHT
-> synchronize srcu/rcu
-> blk_mq_terminate_expired
-> rq->__deadline (J2 + MQ_RQ_IN_FLIGHT)
1. deadline = rq->__deadline & ~RQ_STATE_MASK (0x3)
if J2-J1 < 4 jiffies, we will get the same deadline value.
2. even if we do some bit shift when save and get deadline
if T2 - T1 < time of 1 jiffies, we sill get the same deadline.
Thanks
Jianchao
