> On Jan 31, 2018, at 2:51 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>
>
>
>> On Jan 31, 2018, at 1:52 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>
>> On Wed, Jan 31, 2018 at 1:29 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>
>>>
>>>> On Jan 30, 2018, at 12:02 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>>>
>>>> On Mon, Jan 29, 2018 at 12:24 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>>>
>>>>>
>>>>>> On Jan 29, 2018, at 12:19 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>>>>>
>>>>>> On Fri, Jan 26, 2018 at 4:08 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>>>>>
>>>>>>>
>>>>>>>> On Jan 26, 2018, at 12:13 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>>>>>>>
>>>>>>>> On Fri, Jan 26, 2018 at 2:29 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> On Jan 26, 2018, at 11:05 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>>>>>>>>>
>>>>>>>>>> On Fri, Jan 26, 2018 at 1:23 PM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> On Jan 26, 2018, at 9:24 AM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> Hi Bruce/Chuck,
>>>>>>>>>>>>
>>>>>>>>>>>> There is a problem with nfsd doing a WRITE of size 4093,4094,4095. To
>>>>>>>>>>>> reproduce, mount with RDMA and do a simple dd "dd if=/dev/zero
>>>>>>>>>>>> of=/mnt/testfile bs=4093 count=1". What happens is that nfsd fails to
>>>>>>>>>>>> parse GETATTR after the WRITE in the compound. It fails the operation
>>>>>>>>>>>> with ERR_OP_ILLEGAL.
>>>>>>>>>>>>
>>>>>>>>>>>> The problem happens for the values where XDR round up ends up rounding
>>>>>>>>>>>> up to the page size. I don't know if my fix is the appropriate way to
>>>>>>>>>>>> fix this but with it I don't get the error:
>>>>>>>>>>>>
>>>>>>>>>>>> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
>>>>>>>>>>>> index 2c61c6b..a8489c3 100644
>>>>>>>>>>>> --- a/fs/nfsd/nfs4xdr.c
>>>>>>>>>>>> +++ b/fs/nfsd/nfs4xdr.c
>>>>>>>>>>>> @@ -1289,11 +1289,12 @@ static __be32 nfsd4_decode_opaque(struct nfsd4_compounda
>>>>>>>>>>>>
>>>>>>>>>>>> len = XDR_QUADLEN(write->wr_buflen) << 2;
>>>>>>>>>>>> if (len >= avail) {
>>>>>>>>>>>> - int pages;
>>>>>>>>>>>> + int pages = 0;
>>>>>>>>>>>>
>>>>>>>>>>>> len -= avail;
>>>>>>>>>>>>
>>>>>>>>>>>> - pages = len >> PAGE_SHIFT;
>>>>>>>>>>>> + if (write->wr_buflen >= PAGE_SIZE)
>>>>>>>>>>>> + pages = len >> PAGE_SHIFT;
>>>>>>>>>>>> argp->pagelist += pages;
>>>>>>>>>>>> argp->pagelen -= pages * PAGE_SIZE;
>>>>>>>>>>>> len -= pages * PAGE_SIZE;
>>>>>>>>>>>>
>>>>>>>>>>>> So the problem is the using "len" instead of "write->wr_buflen" leads
>>>>>>>>>>>> for the values 4093,4094,4095 that are rounded up to 4096, it makes
>>>>>>>>>>>> pages=1 and the argp->pagelen ends up being a negative value leading
>>>>>>>>>>>> to problems of parsing the GETATTR.
>>>>>>>>>>>
>>>>>>>>>>> Would this also be a problem near any page boundary, say, a
>>>>>>>>>>> write length of 8191 bytes?
>>>>>>>>>>>
>>>>>>>>>>> Instead of using the rounded up "len", why not try this:
>>>>>>>>>>>
>>>>>>>>>>> - pages = len >> PAGE_SHIFT;
>>>>>>>>>>> + pages = write->wr_buflen >> PAGE_SHIFT;
>>>>>>>>>>
>>>>>>>>>> You are right. It needs to be that. Otherwise 8191 fails the same way.
>>>>>>>>>>
>>>>>>>>>>> And be sure to test with TCP as well.
>>>>>>>>>>
>>>>>>>>>> Sigh. It breaks normal (non-RDMA) mounts. I'll figure out why.
>>>>>>>>>
>>>>>>>>> OK.
>>>>>>>>>
>>>>>>>>> Remember that a Read chunk's length does not have to be
>>>>>>>>> rounded up. Maybe the transport needs to round up the
>>>>>>>>> length of the unmarshaled data content on behalf of the
>>>>>>>>> NFSv4 write decoder.
>>>>>>>>>
>>>>>>>>
>>>>>>>> The problem of simply taking write->wr_buflen was that len before that
>>>>>>>> could have been adjusted by avail value in then non-RDAM mounts.
>>>>>>>>
>>>>>>>> Again, I'm not sure if this is the right fix. But this one works for
>>>>>>>> both non-RDMA and RDMA mounts.
>>>>>>>>
>>>>>>>> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
>>>>>>>> index 2c61c6b..3178997 100644
>>>>>>>> --- a/fs/nfsd/nfs4xdr.c
>>>>>>>> +++ b/fs/nfsd/nfs4xdr.c
>>>>>>>> @@ -1293,7 +1293,10 @@ static __be32 nfsd4_decode_opaque(struct
>>>>>>>> nfsd4_compoundargs *argp, struct xdr_ne
>>>>>>>>
>>>>>>>> len -= avail;
>>>>>>>>
>>>>>>>> - pages = len >> PAGE_SHIFT;
>>>>>>>> + if (!avail)
>>>>>>>> + pages = write->wr_buflen >> PAGE_SHIFT;
>>>>>>>> + else
>>>>>>>> + pages = len >> PAGE_SHIFT;
>>>>>>>> argp->pagelist += pages;
>>>>>>>> argp->pagelen -= pages * PAGE_SIZE;
>>>>>>>> len -= pages * PAGE_SIZE;
>>>>>>>
>>>>>>> This code has been around since 2012. Has it always been
>>>>>>> broken for RDMA? I suspect the root problem is in the
>>>>>>> transport, not here in the decoder. Can you bisect to
>>>>>>> find out where the problem started to occur?
>>>>>>
>>>>>> To see if I could go back to 2012, I first want to see if I could go
>>>>>> back to before mlx5 driver was added which was in 3.11-rc1. But I'm
>>>>>> having issues trying to boot into a kernel based on 3.10 or 3.9. I'm
>>>>>> trying to verify if my CX-5 card would even work with mlx4 driver
>>>>>> which I'm having doubts it would.
>>>>>
>>>>> The CX-5 works only with mlx5.
>>>>>
>>>>>
>>>>>> These old kernels fail to boot in
>>>>>> XFS saying that it's a wrong version. Some googling makes me think
>>>>>> that since my XFS partition was created with a newer kernel it's not
>>>>>> compatible with an older kernel...
>>>>>
>>>>> That's correct, the XFS filesystem has new features like
>>>>> metadata checksum that don't work on older kernels.
>>>>>
>>>>> To start with, you could try some very late 3.x or early
>>>>> 4.x kernels. My intuition is that you will find an svcrdma
>>>>> change that is more recent than 2012 that is causing the
>>>>> underlying issue.
>>>>
>>>> It works in 4.8 and does not work in 4.9. It's this commit that breaks it:
>>>>
>>>> commit cc9d83408b52265ddab2874cf19d1611da4ca7ee
>>>>
>>>> svcrdma: Server-side support for rpcrdma_connect_private
>>>>
>>>> Prepare to receive an RDMA-CM private message when handling a new
>>>> connection attempt, and send a similar message as part of connection
>>>> acceptance.
>>>>
>>>> Both sides can communicate their various implementation limits.
>>>> Implementations that don't support this sideband protocol ignore it.
>>>>
>>>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>>> Reviewed-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
>>>> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>>>>
>>>> So far I don't understand how can causes problems...
>>>
>>> More likely it's:
>>>
>>>
>>> commit eae03e2ac80a3476f0652cb0ee451d7b06d30564
>>> Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>> AuthorDate: Fri Aug 18 11:12:27 2017 -0400
>>> Commit: J. Bruce Fields <bfields@xxxxxxxxxx>
>>> CommitDate: Tue Sep 5 15:15:29 2017 -0400
>>>
>>> nfsd: Incoming xdr_bufs may have content in tail buffer
>>>
>>>
>>>
>>> This is a 3 op compound. The third op is GETATTR.
>>> The reply shows that the WRITE op succeeds, which
>>> is why no error is reported to the application.
>>> The GETATTR fails with OP_ILLEGAL, and the client
>>> I guess is trained to ignore that kind of failure.
>>>
>>> After nfsd4_decode_write pushes into the "next" page
>>> in the page list, the next time READ_BUF is called
>>> (to handle the next op in the compound), it is
>>> supposed to see that the XDR page list is now
>>> exhausted, and switch to the XDR tail buf.
>>>
>>> TCP doesn't use the tail buf; the GETATTR in that
>>> case is at the end of the page list, following the
>>> WRITE payload. That would explain why this issue
>>> cannot be reproduced there.
>>>
>>> RDMA does use the tail buf in this case. For some
>>> reason the logic added in eae03e2ac8 is not working,
>>> and the server is looking at uninitialized memory
>>> to find that third op.
>>>
>>> I run cthon04 all the time, so I wonder why I never
>>> hit this case.
>>
>> While this commit seems like a better explanation, I can 100% hit the
>> issue running 4.8-rc6 based kernel (this is from your nfsd-for-4.9
>> branch and rollback back to the cc9d83408b) . What matters is the
>> assignment of the "private_data" in the conn_param. If I set it to
>> NULL and 0 for the length. The problem goes away.
>
> There's no obvious connection between the NFSv4 WRITE
> misbehavior and CM private data being present.
You observed that this logic in nfsd4_decode_write is
making argp->pagelen go negative:
1304 pages = len >> PAGE_SHIFT;
1305 argp->pagelist += pages;
1306 argp->pagelen -= pages * PAGE_SIZE;
1307 len -= pages * PAGE_SIZE;
This is because the client does not insert XDR round-up
in the Read chunk. Since pagelen is not zero, the code
in read_buf that is looking for that case (added by
eae03e2ac80a) fails.
I suspect what's going on here is:
When you disable the private_data logic, the server is
not "receiving" the CM private data, and thus it assumes
the client is not Linux. In response, the server does not
provide CM private data in it's "connection accept"
response.
The client then assumes the _server_ is not Linux, and
disables an optimization that removes the XDR round-up
from Read chunks.
So the client adds that round-up padding to the end of
the Read chunks, and that prevents the bug. pagelen
never goes below zero.
Basically nfsd4_decode_write() assumes that the XDR
round-up for the WRITE payload is always going to be
present. The round-up is optional for Read chunks,
according to RFC 8166.
193bcb7b37 adds that round-up in the tail iovec. It looks
like that won't be adequate in the case where the payload
approaches a page boundary.
Does this seem plausible?
>> Are you hitting the issue now?
>
> I can reproduce it 100% of the time using your dd example
> from a Linux NFS client.
>
> I've also done a 8009 byte write on TCP, which forces the
> same page boundary edge condition in nfsd4_decode_write,
> and the failure does not occur.
>
>
>> Are you 100% certain that you haven't
>> hit it before. Do you always inspect the network traces? Without
>> inspecting the network trace you wouldn't have found it. cthon never
>> fails so from the user perspective nothing failed.
>
> Fair enough.
>
>
>> I will check eae03e2ac80a3476f0652cb0ee451d7b06d30564 commit to see
>> what different do I see in my testing.
>
> My theory is it's that one or this related one:
>
> commit 193bcb7b3719a315814dce40fc8dcd1af786ea64
> Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
> AuthorDate: Fri Aug 18 11:12:35 2017 -0400
> Commit: J. Bruce Fields <bfields@xxxxxxxxxx>
> CommitDate: Tue Sep 5 15:15:29 2017 -0400
>
> svcrdma: Populate tail iovec when receiving
>
>
>>>>>>>>>>>> If this looks OK, I can send a patch.
>>>>>>>>>>>> --
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>>>>>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
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>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> Chuck Lever
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>>>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>>>>>> --
>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Chuck Lever
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>> --
>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>>>
>>>>>>> --
>>>>>>> Chuck Lever
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>
>>>>> --
>>>>> Chuck Lever
>>>>>
>>>>>
>>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>
>>> --
>>> Chuck Lever
>
> --
> Chuck Lever
>
>
>
> --
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--
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