Accessing the user stack inside system call service routine

[Paul Mackerras]

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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