Problem: say nfsd is not running but the redirector is active already
(ie. start deamon, stop deamon). problem doesn't exist if nfsd has never
been started. now a user process executes a mount command, the kernel
ends up creating a system thread to handle creation of the vnetroot.
that thread places a mount upcall and waits for the down call. now
kill the user process. now start the nfsd. it will pick up a queued up
upcall entry. however, in the arguments there are pointers to server name
and mount point values that are stored in the memory of the user process
that started the mount but now ended.
Solution: check that Mount.srv_name and Mount.root are still valid
addresses before dereferencing them.
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