NFSv4: Don't try to recover NFSv4 locks when they are lost.

When an NFSv4 client loses contact with the server it can lose any
locks that it holds.

Currently when it reconnects to the server it simply tries to reclaim
those locks.  This might succeed even though some other client has
held and released a lock in the mean time.  So the first client might
think the file is unchanged, but it isn't.  This isn't good.

If, when recovery happens, the locks cannot be claimed because some
other client still holds the lock, then we get a message in the kernel
logs, but the client can still write.  So two clients can both think
they have a lock and can both write at the same time.  This is equally
not good.

There was a patch a while ago
  http://comments.gmane.org/gmane.linux.nfs/41917

which tried to address some of this, but it didn't seem to go
anywhere.  That patch would also send a signal to the process.  That
might be useful but for now this patch just causes writes to fail.

For NFSv4 (unlike v2/v3) there is a strong link between the lock and
the write request so we can fairly easily fail any IO of the lock is
gone.  While some applications might not expect this, it is still
safer than allowing the write to succeed.

Because this is a fairly big change in behaviour a module parameter,
"recover_locks", is introduced which defaults to true (the current
behaviour) but can be set to "false" to tell the client not to try to
recover things that were lost.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index da608ee8d5ff..cc14cbb78b73 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -969,7 +969,9 @@ static int nfs4_copy_lock_stateid(nfs4_stateid *dst,
 	fl_pid = lockowner->l_pid;
 	spin_lock(&state->state_lock);
 	lsp = __nfs4_find_lock_state(state, fl_owner, fl_pid, NFS4_ANY_LOCK_TYPE);
-	if (lsp != NULL && test_bit(NFS_LOCK_INITIALIZED, &lsp->ls_flags) != 0) {
+	if (lsp && test_bit(NFS_LOCK_LOST, &lsp->ls_flags))
+		ret = -EIO;
+	else if (lsp != NULL && test_bit(NFS_LOCK_INITIALIZED, &lsp->ls_flags) != 0) {
 		nfs4_stateid_copy(dst, &lsp->ls_stateid);
 		ret = 0;
 		smp_rmb();
@@ -1009,11 +1011,17 @@ static int nfs4_copy_open_stateid(nfs4_stateid *dst, struct nfs4_state *state)
 int nfs4_select_rw_stateid(nfs4_stateid *dst, struct nfs4_state *state,
 		fmode_t fmode, const struct nfs_lockowner *lockowner)
 {
-	int ret = 0;
+	int ret = nfs4_copy_lock_stateid(dst, state, lockowner);
+	if (ret == -EIO)
+		/* A lost lock - don't even consider delegations */
+		goto out;
 	if (nfs4_copy_delegation_stateid(dst, state->inode, fmode))
 		goto out;
-	ret = nfs4_copy_lock_stateid(dst, state, lockowner);
 	if (ret != -ENOENT)
+		/* nfs4_copy_delegation_stateid() didn't over-write
+		 * dst, so it still has the lock stateid which we now
+		 * choose to use.
+		 */
 		goto out;
 	ret = nfs4_copy_open_stateid(dst, state);
 out: