I agree that a mount option to override maxmpx would be useful
(and preferable to the existing module param - a default value overridable
at insmod time is harder than at mount time) - especially useful to Samba
server which IIRC can handle more than 50 simultaneous requests
but does not advertise this support in its negotiate response.
On Wed, Jul 6, 2011 at 12:50 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Wed, 6 Jul 2011 12:35:27 -0500
> Steve French <smfrench@xxxxxxxxx> wrote:
>
>> I have reviewed/merged two of Jeffs 4 recent patches (still reviewing
>> the last two)
>>
>> On the problem with WindowsXP mounts limiting the number of
>> simultaneous requests and timing out when large numbers are sent in
>> parallel (especially when doing large numbers of small writes at one
>> time) - I am running ok with this patch and did discuss briefly with
>> Jeff. I would rather not do a more invasive patch (if possible) -
>> this leaves the behavior as is except for servers which specify an mpx
>> under 50 which is reasonable (ie at least 2) - otherwise it should
>> work identically, and it seems to fix the XP problem.
>>
>> commit a30b9327eb4543d45ffb79ebbcabe251eb6a3b9c
>> Author: Steve French <sfrench@xxxxxxxxxx>
>> Date: Fri Jul 1 12:47:23 2011 -0500
>>
>> [CIFS] Limit simultaneous requests to older servers which set maxmpx low
>>
>> WindowsXP (at least some service packs) sets the maximum number of
>> simultaneous
>> requests to 10 which is smaller than most servers (almost all set
>> the limit at 50) and the cifs client set it to, and when
>> about 30 requests or so are in flight, requests to WindowsXP servers can
>> time out, especially with the new cifs async write code
>> which frequently dispatches larger numbers of requests in parallel
>> than in previous versions of cifs.
>>
>> Limit the number of simultaneous requests to what the server
>> sets unless server reports an implausible number (must be a minimum of 2
>> to allow for a request and oplock break).
>>
>> Signed-off-by: Steve French <smfrench@xxxxxxxxxx>
>>
>> diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
>> index 1a9fe7f..1957f5d 100644
>> --- a/fs/cifs/cifssmb.c
>> +++ b/fs/cifs/cifssmb.c
>> @@ -453,6 +453,11 @@ CIFSSMBNegotiate(unsigned int xid, struct cifs_ses *ses)
>> }
>> server->sec_mode = (__u8)le16_to_cpu(rsp->SecurityMode);
>> server->maxReq = le16_to_cpu(rsp->MaxMpxCount);
>> + /* maxReq must be at least 2, almost all servers set to 50,
>> + some old non-MS servers set incorrectly so set to default
>> + (otherwise oplock break e.g. would fail */
>> + if (server->maxReq < 2)
>> + server->maxReq = CIFS_MAX_REQ; /* 50 */
>> server->maxBuf = min((__u32)le16_to_cpu(rsp->MaxBufSize),
>> (__u32)CIFSMaxBufSize + MAX_CIFS_HDR_SIZE);
>> server->max_vcs = le16_to_cpu(rsp->MaxNumberVcs);
>> @@ -560,6 +565,11 @@ CIFSSMBNegotiate(unsigned int xid, struct cifs_ses *ses)
>> /* one byte, so no need to convert this or EncryptionKeyLen from
>> little endian */
>> server->maxReq = le16_to_cpu(pSMBr->MaxMpxCount);
>> + /* maxReq must be at least 2, almost all servers set to 50,
>> + some old non-MS servers set incorrectly so set to default
>> + (otherwise oplock break e.g. would fail */
>> + if (server->maxReq < 2)
>> + server->maxReq = CIFS_MAX_REQ; /* 50 */
>> /* probably no need to store and check maxvcs */
>> server->maxBuf = min(le32_to_cpu(pSMBr->MaxBufferSize),
>> (__u32) CIFSMaxBufSize + MAX_CIFS_HDR_SIZE);
>> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
>> index 147aa22..e2bd2a9 100644
>> --- a/fs/cifs/transport.c
>> +++ b/fs/cifs/transport.c
>> @@ -264,7 +264,13 @@ static int wait_for_free_request(struct
>> TCP_Server_Info *server,
>>
>> spin_lock(&GlobalMid_Lock);
>> while (1) {
>> - if (atomic_read(&server->inFlight) >= cifs_max_pending) {
>> + /* We must check that don't exceed maxReq but on SMB Negotiate
>> + it is not initted yet (maxReq must be at least two) */
>> + /* Could also check if oplock enabled but how could turn off? */
>> + if ((atomic_read(&server->inFlight) >= cifs_max_pending) ||
>> + ((atomic_read(&server->inFlight) + 1 >= server->maxReq) &&
>> + (server->maxReq > 1))) {
>> spin_unlock(&GlobalMid_Lock);
>> #ifdef CONFIG_CIFS_STATS2
>> atomic_inc(&server->num_waiters);
>>
>
> I'm ok with this hack as an interim thing. Long term I think it would
> make more sense to fail the mount when the server sends us a bogus
> value here, and allow the admin to override that value via some other
> means -- maybe a mount option or something.
>
> FWIW, MS-CIFS says this:
>
> -----------------------[snip]------------------------
>
> MaxMpxCount (2 bytes): The maximum number of outstanding SMB operations
> that the server supports. This value includes existing OpLocks, the
> NT_TRANSACT_NOTIFY_CHANGE subcommand, and any other commands that are
> pending on the server. If the negotiated MaxMpxCount is 0x0001, then
> OpLock support MUST be disabled for this session. The MaxMpxCount MUST
> be greater than 0x0000. This parameter has no specific relationship to
> the SMB_COM_READ_MPX and SMB_COM_WRITE_MPX commands.
>
> -----------------------[snip]------------------------
>
> I think we ought to try and follow the letter of the spec here, though
> I'm unclear on what they mean by "existing Oplocks" -- do they mean
> we're supposed to hold one of these slots in reserve for every oplock
> we hold? That could be ugly. In any case, as far as 3.0 goes...
>
> Meh-I-guess-its-better-than-nothing-by: Jeff Layton <jlayton@xxxxxxxxxx>
>
--
Thanks,
Steve
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