NFSv4.1 Fix a pNFS session draining deadlock

On a CB_RECALL the callback service thread flushes the inode using
filemap_flush prior to scheduling the state manager thread to return the
delegation. When pNFS is used and I/O has not yet gone to the data server
servicing the inode, a LAYOUTGET can preceed the I/O. Unlike the async
filemap_flush call, the LAYOUTGET must proceed to completion.

If the state manager starts to recover data while the inode flush is sending
the LAYOUTGET, a deadlock occurs as the callback service thread holds the
single callback session slot until the flushing is done which blocks the state
manager thread, and the state manager thread has set the session draining bit
which puts the inode flush LAYOUTGET RPC to sleep on the forechannel slot
table waitq.

Separate the draining of the back channel from the draining of the fore channel
by moving the NFS4_SESSION_DRAINING bit from session scope into the fore
and back slot tables.  Drain the back channel first allowing the LAYOUTGET
call to proceed (and fail) so the callback service thread frees the callback
slot. Then proceed with draining the forechannel.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/nfs/nfs4session.c b/fs/nfs/nfs4session.c
index ebda5f4a031b..c4e225e4a9af 100644
--- a/fs/nfs/nfs4session.c
+++ b/fs/nfs/nfs4session.c
@@ -73,7 +73,7 @@ void nfs4_free_slot(struct nfs4_slot_table *tbl, struct nfs4_slot *slot)
 			tbl->highest_used_slotid = new_max;
 		else {
 			tbl->highest_used_slotid = NFS4_NO_SLOT;
-			nfs4_session_drain_complete(tbl->session, tbl);
+			nfs4_slot_tbl_drain_complete(tbl);
 		}
 	}
 	dprintk("%s: slotid %u highest_used_slotid %d\n", __func__,
@@ -226,7 +226,7 @@ static bool nfs41_assign_slot(struct rpc_task *task, void *pslot)
 	struct nfs4_slot *slot = pslot;
 	struct nfs4_slot_table *tbl = slot->table;
 
-	if (nfs4_session_draining(tbl->session) && !args->sa_privileged)
+	if (nfs4_slot_tbl_draining(tbl) && !args->sa_privileged)
 		return false;
 	slot->generation = tbl->generation;
 	args->sa_slot = slot;