Messages in this thread Patch in this message | | | Date | Fri, 15 Apr 2005 02:23:31 +0200 (CEST) | From | Jesper Juhl <> | Subject | Re: [PATCH] sched: fix never executed code due to expression always false |
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On Fri, 15 Apr 2005, Nick Piggin wrote:
> Jesper Juhl wrote: > > On Fri, 15 Apr 2005, Nick Piggin wrote: > > > > > > > Jesper Juhl wrote: > > > > > > > There are two expressions in kernel/sched.c that are always false since > > > > they > > > > test for <0 but the result of the expression is unsigned so they will > > > > never > > > > be less than zero. This patch implement the logic that I believe is > > > > intended > > > > without the signedness issue and without the nasty casts. > > > > <disclaimer>patch is compile tested only</disclaimer> > > > > > > > This is not *quite* the intended behaviour. It is OK for prev->timestamp > > > to be '0 - a bit' and now to be '0 + a bit' in the case of wrapping. > > > > > > Although considering they're 64-bit values, I'm not sure how much we care. > > > > > > > How do you propose to fix this then? As the code is now the expressionsa > > are always false - should we just remove the them? Or do you have a > > sensible definition of "a bit" ? or ome other suggestion alltogether? > > > > Make it a signed comparison? > As per this patch perhaps? :
Signed-off-by: Jesper Juhl <juhl-lkml@dif.dk>
--- linux-2.6.12-rc2-mm3-orig/kernel/sched.c 2005-04-11 21:20:56.000000000 +0200 +++ linux-2.6.12-rc2-mm3/kernel/sched.c 2005-04-15 02:21:34.000000000 +0200 @@ -2697,9 +2697,10 @@ need_resched_nonpreemptible: schedstat_inc(rq, sched_cnt); now = sched_clock(); if (likely((long long)now - prev->timestamp < NS_MAX_SLEEP_AVG)) { - run_time = now - prev->timestamp; - if (unlikely((long long)now - prev->timestamp < 0)) + if (unlikely(((long long)now - (long long)prev->timestamp) < 0)) run_time = 0; + else + run_time = now - prev->timestamp; } else run_time = NS_MAX_SLEEP_AVG; @@ -2776,7 +2777,7 @@ go_idle: if (!rt_task(next) && next->activated > 0) { unsigned long long delta = now - next->timestamp; - if (unlikely((long long)now - next->timestamp < 0)) + if (unlikely(((long long)now - (long long)next->timestamp) < 0)) delta = 0; if (next->activated == 1)
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