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git2svn
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V 27
2021-03-15T20:51:07.218926Z
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V 912
nfsclient: add nfs node locking around uses of n_direofoffset

During code inspection I noticed that the n_direofoffset field
of the NFS node was being manipulated without any lock being
held to make it SMP safe.
This patch adds locking of the NFS node's mutex around
handling of n_direofoffset to make it SMP safe.

I have not seen any failure that could be attributed to n_direofoffset
being manipulated concurrently by multiple processors, but I think this
is possible, since directories are read with shared vnode
locking, plus locks only on individual buffer cache blocks.
However, there have been as yet unexplained issues w.r.t reading
large directories over NFS that could have conceivably been caused
by concurrent manipulation of n_direofoffset.

(cherry picked from commit 15bed8c46b32dec19e922cb89e12c8970867a303)

Git Hash:   a1224bee90c6a54909d279ec631ea2ad8241ddf4
Git Author: rmacklem@FreeBSD.org
END