On 13 Nov 2016, at 8:34, Benjamin Coddington wrote:
On 12 Nov 2016, at 21:56, Jeff Layton wrote:
On Sat, 2016-11-12 at 16:16 -0500, Jeff Layton wrote:
On Sat, 2016-11-12 at 13:03 -0500, Benjamin Coddington wrote:
On 12 Nov 2016, at 11:52, Jeff Layton wrote:
On Sat, 2016-11-12 at 10:31 -0500, Benjamin Coddington wrote:
On 12 Nov 2016, at 7:54, Jeff Layton wrote:
On Sat, 2016-11-12 at 06:08 -0500, Benjamin Coddington wrote:
I've been seeing the following on a modified version of
generic/089
that gets the client stuck sending LOCK with
NFS4ERR_OLD_STATEID.
1. Client has open stateid A, sends a CLOSE
2. Client sends OPEN with same owner
3. Client sends another OPEN with same owner
4. Client gets a reply to OPEN in 3, stateid is B.2 (stateid B
sequence 2)
5. Client does LOCK,LOCKU,FREE_STATEID from B.2
6. Client gets a reply to CLOSE in 1
7. Client gets reply to OPEN in 2, stateid is B.1
8. Client sends LOCK with B.1 - OLD_STATEID, now stuck in a
loop
The CLOSE response in 6 causes us to clear NFS_OPEN_STATE, so
that
the OPEN
response in 7 is able to update the open_stateid even though it
has a
lower
sequence number.
I think this case could be handled by never updating the
open_stateid
if the
stateids match but the sequence number of the new state is less
than
the
current open_state.
What kernel is this on?
On v4.9-rc2 with a couple fixups. Without them, I can't test
long
enough to
reproduce this race. I don't think any of those are involved in
this
problem, though.
Yes, that seems wrong. The client should be picking B.2 for the
open
stateid to use. I think that decision of whether to take a seqid
is
made
in nfs_need_update_open_stateid. The logic in there looks
correct to
me
at first glance though.
nfs_need_update_open_stateid() will return true if NFS_OPEN_STATE
is
unset.
That's the precondition set up by steps 1-6. Perhaps it should
not
update
the stateid if they match but the sequence number is less, and
still set
NFS_OPEN_STATE once more. That will fix _this_ case. Are there
other
cases
where that would be a problem?
Ben
That seems wrong.
I'm not sure what you mean: what seems wrong?
Sorry, it seems wrong that the client would issue the LOCK with B.1
there.
The only close was sent in step 1, and that was for a
completely different stateid (A rather than B). It seems likely
that
that is where the bug is.
I'm still not sure what point you're trying to make..
Even though the close was sent in step 1, the response wasn't
processed
until step 6..
Not really a point per-se, I was just saying where I think the bug
might
be...
When you issue a CLOSE, you issue it vs. a particular stateid
(stateid
"A" in this case). Once the open stateid has been superseded by "B",
the
closing of "A" should have no effect.
Perhaps nfs_clear_open_stateid needs to check and see whether the
open
stateid has been superseded before doing its thing?
Ok, I see something that might be a problem in this call in
nfs4_close_done:
nfs_clear_open_stateid(state, &calldata->arg.stateid,
res_stateid,
calldata->arg.fmode);
Note that we pass two nfs4_stateids to this call. The first is the
stateid that got sent in the CLOSE call, and the second is the
stateid
that came back in the CLOSE response.
RFC5661 and RFC7530 both indicate that the stateid in a CLOSE
response
should be ignored.
So, I think a patch like this may be in order. As to whether it will
fix this bug, I sort of doubt it, but it might not hurt to test it
out?
Doesn't this undo the fix in 4a1e2feb9d24 ("NFSv4.1: Fix a protocol
issue
with CLOSE stateids")?
I don't think it will help with the race either, since I think the
issue is
that the race above unsets NFS_OPEN_STATE, then that is reason enough
to
overwrite the existing open_state, even if it is going to overwrite
with an
older stateid. What close does with its stateid is unimportant to
that
problem.
In the interest of science, I'll kick off a test with this patch. It
should
take a few hours to reproduce, but I'm also fairly busy today, so I'll
report back this evening most likely. Thanks for the patch.
I got lucky and it reproduced in about 10 minutes with this patch.
Ben
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