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SubjectRe: 2.6.16-rc4: known regressions


On Wed, 22 Feb 2006, Greg KH wrote:
>
> RHEL is a very different kernel from mainline (just like SLES is). Have
> you looked through their patches to see if they are including something
> that causes this behavior?

Quite apart from that, we have definitely had issues where pure timing
makes a difference - the kernel does the same exact thing, but just
switches the order of some driver initialization, so that when /sbin/init
starts, some discovery is still on-going.

It's _rare_, but it's one kind of bug that the kernel really can't do a
lot about. For example, for the longest time we held off from the
scheduler running child programs before returning to the parent after a
fork(), simply because that triggered a real race condition in "bash".

Eventually, we could say "screw it, it's a user-level timing bug", but the
point being that sometimes timing changes, and while we _can_ try to keep
even timing-related behaviour like that similar, sometimes it just isn't
possible.

It's quite possible that nothing has really "changed", and that some part
of the kernel just finishes more quickly (or slowly), triggering this
problem.

Linus
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