Steffen Rumler writes:

The copy_from_user() works fine. The printk() message does not
appear.

The copy_from_user call looks correct to me.

Later, when I inspect 'current->user_stack_xxx' (temporary
added to struct_task) for all processes with 'current->in_suspend'
set, all seems to be zero. I do this check within a kernel
module, I can load when the threads are hanging.

That is indeed very strange.  The first word should be non-zero at the
very least.  Is it possible that your program has in fact trashed its
stack?  Another thing to try would be to check the contents of
current->user_stack_xxx immediately after you copy it to see whether
it is all zero at that point.

Paul.

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