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SubjectRe: BUG: Global FPU corruption in 2.2
On Thu, Apr 19, 2001 at 11:05:03AM -0500, Victor Zandy wrote:
>
> We have found that one of our programs can cause system-wide
> corruption of the x86 FPU under 2.2.16 and 2.2.17. That is, after we
> run this program, the FPU gives bad results to all subsequent
> processes.

A few comments, not sure if they will help very much:

1.) If I'm not mistaken switch_to changes current->flags without
atomic operations and without any locks and sys_ptrace changes
child->flags only protected by the big kernel lock.
I could imagine that this causes local corruption on an SMP machine
and this is something that changed in 2.4 kernels, but I don't see
how this can corrupt FPU state globally. Maybe there is something else.

2.) I guess a single finit (as proposed by someone else in this thread)
won't assure that both FPUs are in a sane state.

3.) It might be interesting to know if the problem can be triggered:
a) If pi doesn't fork, i.e. just one process calculating pi and
another one doing the attach/detach.
b) If pi doesn't do FPU Operations, i.e. only the children call do_pi.

regards Christian

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