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SubjectRe: [patch] jiffies wraparound [Re: 2.1.125 Show stopper list: Draft]

On Sun, 18 Oct 1998, Alan Cox wrote:

> 1.2 survives mostly, 2.0 survives mostly, 2.1.x doesnt survive

while being correct isnt the issue for 2.2, not hanging on a wraparound
would be nice to have. Theres another problematic area, 'task->timeout'
usage. The basic problem is that ->timeout is measured in absolute
jiffies, instead of delta. timeout == -1 is used as an indicator of 'never
time out', which is incorrect if we are near to a wraparound. Also,
timeout == 0 is internally used as 'no manual timeout for this process',
which is also incorrect when we wrap around.

these problems could as well result in a timer not being set, so this
could theoretically explain the tty problems on wraparound as well.

the right thing i think is a 'delta' timeout instead of an absolute
timeout, but this is definitely not a 2.2 issue. Since most places
artifically add 'jiffies' to some delta timeout anyway before setting
current->timeout, this looks clean as well.

-- mingo


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