Fix the race of dereferencing /proc/<pid>/file with execve(2) by caching the value of p_textvp. This way, we always unlock the locked vnode. While there, vhold() the vnode around the vn_lock().
Fix the race of dereferencing /proc/<pid>/file with execve(2) by caching
the value of p_textvp. This way, we always unlock the locked vnode.
While there, vhold() the vnode around the vn_lock().

Reported and tested by:	Guy Helmer (ghelmer palisadesys com)
Approved by:		des (procfs maintainer)
MFC after:		1 week

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