K 10
svn:author
V 8
hselasky
K 8
svn:date
V 27
2015-10-29T13:53:37.047101Z
K 7
svn:log
V 473
Add missing NULL check in physio().

When destroying a character device the si_devsw field is set to NULL
before all references are gone, to indicate the character device is
going away. This can cause a NULL-dereference fault inside physio().

The callers of physio() should own a thread reference on the cdev and
if si_devsw is seen as non-NULL, it is usable during the execution of
the function. Else an ENXIO error code is returned.

Reviewed by:	kib
MFC after:	2 weeks

END