Re: [PATCH RFC v6 2/2] nfsd: Initial implementation of NFSv4 Courteous Server

[dai.ngo@oracle.com]

On 12/8/21 8:16 AM, Trond Myklebust wrote:
> On Wed, 2021-12-08 at 07:54 -0800, dai.ngo@oracle.com wrote:
>> On 12/6/21 11:55 AM, Chuck Lever III wrote:
>>
>>>> +
>>>> +/*
>>>> + * Function to check if the nfserr_share_denied error for 'fp'
>>>> resulted
>>>> + * from conflict with courtesy clients then release their state to
>>>> resolve
>>>> + * the conflict.
>>>> + *
>>>> + * Function returns:
>>>> + *      0 -  no conflict with courtesy clients
>>>> + *     >0 -  conflict with courtesy clients resolved, try
>>>> access/deny check again
>>>> + *     -1 -  conflict with courtesy clients being resolved in
>>>> background
>>>> + *            return nfserr_jukebox to NFS client
>>>> + */
>>>> +static int
>>>> +nfs4_destroy_clnts_with_sresv_conflict(struct svc_rqst *rqstp,
>>>> +                       struct nfs4_file *fp, struct
>>>> nfs4_ol_stateid *stp,
>>>> +                       u32 access, bool share_access)
>>>> +{
>>>> +       int cnt = 0;
>>>> +       int async_cnt = 0;
>>>> +       bool no_retry = false;
>>>> +       struct nfs4_client *cl;
>>>> +       struct list_head *pos, *next, reaplist;
>>>> +       struct nfsd_net *nn = net_generic(SVC_NET(rqstp),
>>>> nfsd_net_id);
>>>> +
>>>> +       INIT_LIST_HEAD(&reaplist);
>>>> +       spin_lock(&nn->client_lock);
>>>> +       list_for_each_safe(pos, next, &nn->client_lru) {
>>>> +               cl = list_entry(pos, struct nfs4_client, cl_lru);
>>>> +               /*
>>>> +                * check all nfs4_ol_stateid of this client
>>>> +                * for conflicts with 'access'mode.
>>>> +                */
>>>> +               if (nfs4_check_deny_bmap(cl, fp, stp, access,
>>>> share_access)) {
>>>> +                       if (!test_bit(NFSD4_COURTESY_CLIENT, &cl-
>>>>> cl_flags)) {
>>>> +                               /* conflict with non-courtesy
>>>> client */
>>>> +                               no_retry = true;
>>>> +                               cnt = 0;
>>>> +                               goto out;
>>>> +                       }
>>>> +                       /*
>>>> +                        * if too many to resolve synchronously
>>>> +                        * then do the rest in background
>>>> +                        */
>>>> +                       if (cnt > 100) {
>>>> +                               set_bit(NFSD4_DESTROY_COURTESY_CLIE
>>>> NT, &cl->cl_flags);
>>>> +                               async_cnt++;
>>>> +                               continue;
>>>> +                       }
>>>> +                       if (mark_client_expired_locked(cl))
>>>> +                               continue;
>>>> +                       cnt++;
>>>> +                       list_add(&cl->cl_lru, &reaplist);
>>>> +               }
>>>> +       }
>>> Bruce suggested simply returning NFS4ERR_DELAY for all cases.
>>> That would simplify this quite a bit for what is a rare edge
>>> case.
>> If we always do this asynchronously by returning NFS4ERR_DELAY
>> for all cases then the following pynfs tests need to be modified
>> to handle the error:
>>
>> RENEW3   st_renew.testExpired                                     :
>> FAILURE
>> LKU10    st_locku.testTimedoutUnlock                              :
>> FAILURE
>> CLOSE9   st_close.testTimedoutClose2                              :
>> FAILURE
>>
>> and any new tests that opens file have to be prepared to handle
>> NFS4ERR_DELAY due to the lack of destroy_clientid in 4.0.
>>
>> Do we still want to take this approach?
> NFS4ERR_DELAY is a valid error for both CLOSE and LOCKU (see RFC7530
> section 13.2 https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/rfc7530*section-13.2__;Iw!!ACWV5N9M2RV99hQ!f8vZHAJophxXdSSJvnxDCSBSRpWFxEOZBo2ZLvjPzXLVrvMYR8RKcc0_Jvjhng$
> ) so if pynfs complains, then it needs fixing regardless.
>
> RENEW, on the other hand, cannot return NFS4ERR_DELAY, but why would it
> need to? Either the lease is still valid, or else someone is already
> trying to tear it down due to an expiration event. I don't see why
> courtesy locks need to add any further complexity to that test.

RENEW fails in the 2nd open:

     c.create_confirm(t.word(), access=OPEN4_SHARE_ACCESS_BOTH,
                      deny=OPEN4_SHARE_DENY_BOTH)     <<======   DENY_BOTH
     sleeptime = c.getLeaseTime() * 2
     env.sleep(sleeptime)
     c2 = env.c2
     c2.init_connection()
     c2.open_confirm(t.word(), access=OPEN4_SHARE_ACCESS_READ,    <<=== needs to handle NFS4ERR_DELAY
                     deny=OPEN4_SHARE_DENY_NONE)

CLOSE and LOCKU also fail in the OPEN, similar to the RENEW test.
Any new pynfs 4.0 test that does open might get NFS4ERR_DELAY.

-Dai