At Connectathon 2016, we found that recent upstream Linux clients
would occasionally send a LOCK operation with a zero stateid. This
appeared to happen in close proximity to another thread returning
a delegation before unlinking the same file while it remained open.
Earlier, the client received a write delegation on this file and
returned the open stateid. Now, as it is getting ready to unlink the
file, it returns the write delegation. But there is still an open
file descriptor on that file, so the client must OPEN the file
again before it returns the delegation.
Since commit 24311f884189 ('NFSv4: Recovery of recalled read
delegations is broken'), nfs_open_delegation_recall() clears the
NFS_DELEGATED_STATE flag _before_ it sends the OPEN. This allows a
racing LOCK on the same inode to be put on the wire before the OPEN
operation has returned a valid open stateid.
After the OPEN(CLAIM_DELEG_CUR_FH) returns, the client holds both
a write delegation and a valid open stateid. It is safe to clear
NFS_DELEGATED_STATE at that point, allowing fresh lock requests
to go on the wire using the newly acquired open stateid.
I'm not certain of this fix. nfs4_handle_delegation_recall_error()
is called from both nfs_open_delegation_recall() and
nfs_lock_delegation_recall(). Is it safe and correct to clear
NFS_DELEGATED_STATE after success in both of these code paths?
Fixes: 24311f884189 ('NFSv4: Recovery of recalled read ...')
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
fs/nfs/nfs4proc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 01bef06..3ccdc76 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -1794,10 +1794,12 @@ static int nfs4_handle_delegation_recall_error(struct nfs_server *server, struct
default:
printk(KERN_ERR "NFS: %s: unhandled error "
"%d.\n", __func__, err);
+ break;
case 0:
case -ENOENT:
case -EAGAIN:
case -ESTALE:
+ clear_bit(NFS_DELEGATED_STATE, &state->flags);
break;
case -NFS4ERR_BADSESSION:
case -NFS4ERR_BADSLOT:
@@ -1857,7 +1859,6 @@ int nfs4_open_delegation_recall(struct nfs_open_context *ctx,
write_seqlock(&state->seqlock);
nfs4_stateid_copy(&state->stateid, &state->open_stateid);
write_sequnlock(&state->seqlock);
- clear_bit(NFS_DELEGATED_STATE, &state->flags);
switch (type & (FMODE_READ|FMODE_WRITE)) {
case FMODE_READ|FMODE_WRITE:
case FMODE_WRITE:
--
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