K 10
svn:author
V 8
rmacklem
K 8
svn:date
V 27
2021-11-18T01:03:32.148611Z
K 7
svn:log
V 1436
nfscl: Add setting n_localmodtime to the Write RPC code

Similar to commit 2be417843a, I believe there could be a race between
the NFS client VOP_LOOKUP() and file Writing that could result in stale
file attributes being loaded into the NFS vnode by VOP_LOOKUP().

I have not been able to reproduce a failure due to this race, but
I believe that there are two possibilities:

The Lookup RPC happens while VOP_WRITE() is being executed and loads
stale file attributes after VOP_WRITE() returns when it has already
completed the Write/Commit RPC(s).
--> For this case, setting the local modify timestamp at the end of
  VOP_WRITE() should ensure that stale file attributes are not loaded.

The Lookup RPC occurs after VOP_WRITE() has returned, while
asynchronous Write/Commit RPCs are in progress and then is
blocked by the vnode held by VOP_OPEN/VOP_CLOSE/VOP_FSYNC which
will flush writes via ncl_flush() or ncl_vinvalbuf(), clearing the
NMODIFIED flag (which indicates Writes-in-progress). The VOP_LOOKUP()
then acquires the NFS vnode lock and fills in stale file attributes.
 --> Setting the local modify timestamp in ncl_flsuh() and ncl_vinvalbuf()
   when they clear NMODIFIED should ensure that stale file attributes
   are not loaded.

This patch does the above.

PR:	259071
(cherry picked from commit 50dcff0816e5e4aa94f51ce27da5121e49902996)

Git Hash:   d472d0358e8fe27c1b1050564cdbd9082bd06a05
Git Author: rmacklem@FreeBSD.org
END