[PATCH 0/5] 2.6.21-rc7 NFS writes: fix a series of issues

[Trond Myklebust <Trond.Myklebust@netapp.com>]

I've split the issues introduced by the 2.6.21-rcX write code up into 4
subproblems.

The first patch is just a cleanup in order to ease review.

Patch number 2 ensures that we never release the PG_writeback flag until
_after_ we've either discarded the unstable request altogether, or put it
on the nfs_inode's commit or dirty lists.

Patch number 3 fixes the 'desynchronized value of nfs_i.ncommit' error. It
uses the PG_NEED_COMMIT flag as an indicator for whether or not the request
may be redirtied.

Patch number 4 protects the NFS '.set_page_dirty' address_space operation
against races with nfs_inode_add_request.

Finally, patch number 5 fixes an issue with the RPC code that is supposed
ensure that NFSv4 disconnects before resending a request. The current code
will disconnect for every request it resends (and has a bunch of false
positive cases), instead of just ensuring that it disconnects once every
time a timeout or a garbage reply occurs.

My thanks to the various patient victim^Wpeople who helped with extensive
testing.

Cheers
  Trond