nfscl: Fix oddball cases for session slot releaseHEADmain

We have identified some cases where silent slot loss can occur
when operations on NFS mounts are aborted. We experience this
when using NFSv4.2, but it likely also occurs with NFSv4.1.

A slot is acquired for compound operations by nfsv4_setsequence()
and freed by newnfs_request(). Any call path that abandons the
compound before reaching newnfs_request() loses the slot permanently.

We identified four call sites where this happens, one of
which where it actually does happen for us in a semi-reproducible
way, which allowed us to develop a candidate patch, attached.

The patch adds one function, nfsv4_freeunsentslot(), to
nfs_clcomsubs.c. It is called from each of the four call
sites: nfsrpc_writerpc(), nfsrpc_writeds(), and two in
nfsrpc_setextattr().

nfsv4_freeunsentslot() calls nfsv4_freeslot() with resetseq
set to true because the aborted RPC will never be sent and
therefore the slot sequence ID should not advance.

With this patch and other diagnostics, we have confirmed
that slot loss does not occur under the conditions that
otherwise cause it in our environment.

PR:	298416
Reviewed by:	rmacklem
MFC after:	1 week

0 files changed, 0 insertions, 0 deletions