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    SubjectRe: [PATCH 1/4] fs/autofs: Use time_before, time_before_eq, etc.
    Ray Lee wrote:
    > On Dec 26, 2007 7:21 AM, Julia Lawall <julia@diku.dk> wrote:
    >> - if (jiffies - ent->last_usage < timeout)
    >> + if (time_before(jiffies, ent->last_usage + timeout))
    >
    > I don't think this is a safe change? subtraction is always safe (if
    > you think about it as 'distance'), addition isn't always safe unless
    > you know the range. The time_before macro will expand that out to
    > (effectively):
    >
    > if ( (long)(ent->last_usage + timeout) - (long)(jiffies) < 0 )
    >
    > which seems to introduce an overflow condition in the first term.
    >
    > Dunno, I may be wrong (happens often), but at the very least what
    > you've transformed it into is no longer obviously correct, and so it's
    > not a great change.

    Indeed. The bottom form will have overflow issues at time
    jiffies_wraparound/2, whereas the top form will have overflow issues
    only near jiffies_wraparound/1.

    -hpa


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