Re: [net-next PATCH v2 5/8] net: Track start of busy loop instead of when it should end

[Eric Dumazet]

On Thu, 2017-03-23 at 22:55 -0700, Alexander Duyck wrote:

> Right, but time_after assumes roll over.  When you are using a time
> value based off of local_clock() >> 10, you don't ever roll over when
> you do addition.  Just the clock rolls over.  At least on 64 bit
> systems.
> 
> So if local time approaches something like all 1's, and we have
> shifted it by 10 it is then the max it can ever reach is
> 0x003FFFFFFFFFFFFF.  I can add our loop time to that and it won't roll
> over.  In the mean time the busy_loop_us_ can never exceed whatever I
> added to that so we are now locked into a loop.  I realize I am
> probably being pedantic, and it will have an exceedingly small rate of
> occurrence, but it is still an issue.

Do you realize that a 64bit clock wont rollover before the host has
reached 584 years of uptime ?