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Message-ID: <2097dca1-78e1-44d8-aeb6-d46b94a63078@oracle.com>
Date: Thu, 2 Oct 2025 11:09:07 -0400
From: Chuck Lever <chuck.lever@...cle.com>
To: Li Lingfeng <lilingfeng3@...wei.com>
Cc: yukuai1@...weicloud.com, houtao1@...wei.com, yi.zhang@...wei.com,
yangerkun@...wei.com, lilingfeng@...weicloud.com,
zhangjian496@...wei.com, bcodding@...hat.com,
linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
tom@...pey.com, Dai.Ngo@...cle.com, neil@...wn.name,
jlayton@...nel.org, okorniev@...hat.com
Subject: Re: [PATCH v3] nfsd: remove long-standing revoked delegations by
force
On 9/29/25 3:40 PM, Chuck Lever wrote:
> On 9/4/25 7:48 PM, Li Lingfeng wrote:
>> When file access conflicts occur between clients, the server recalls
>> delegations. If the client holding delegation fails to return it after
>> a recall, nfs4_laundromat adds the delegation to cl_revoked list.
>> This causes subsequent SEQUENCE operations to set the
>> SEQ4_STATUS_RECALLABLE_STATE_REVOKED flag, forcing the client to
>> validate all delegations and return the revoked one.
>>
>> However, if the client fails to return the delegation like this:
>> nfs4_laundromat nfsd4_delegreturn
>> unhash_delegation_locked
>> list_add // add dp to reaplist
>> // by dl_recall_lru
>> list_del_init // delete dp from
>> // reaplist
>> destroy_delegation
>> unhash_delegation_locked
>> // do nothing but return false
>> revoke_delegation
>> list_add // add dp to cl_revoked
>> // by dl_recall_lru
>>
>> The delegation will remain in the server's cl_revoked list while the
>> client marks it revoked and won't find it upon detecting
>> SEQ4_STATUS_RECALLABLE_STATE_REVOKED.
>> This leads to a loop:
>> the server persistently sets SEQ4_STATUS_RECALLABLE_STATE_REVOKED, and the
>> client repeatedly tests all delegations, severely impacting performance
>> when numerous delegations exist.
>>
>> Since abnormal delegations are removed from flc_lease via nfs4_laundromat
>> --> revoke_delegation --> destroy_unhashed_deleg -->
>> nfs4_unlock_deleg_lease --> kernel_setlease, and do not block new open
>> requests indefinitely, retaining such a delegation on the server is
>> unnecessary.
>>
>> Fixes: 3bd64a5ba171 ("nfsd4: implement SEQ4_STATUS_RECALLABLE_STATE_REVOKED")
>> Reported-by: Zhang Jian <zhangjian496@...wei.com>
>> Closes: https://lore.kernel.org/all/ff8debe9-6877-4cf7-ba29-fc98eae0ffa0@huawei.com/
>> Signed-off-by: Li Lingfeng <lilingfeng3@...wei.com>
>> Reviewed-by: Jeff Layton <jlayton@...nel.org>
>> ---
>> Changes in v2:
>> 1) Set SC_STATUS_CLOSED unconditionally in destroy_delegation();
>> 2) Determine whether to remove the delegation based on SC_STATUS_CLOSED,
>> rather than by timeout;
>> 3) Modify the commit message.
>>
>> Changes in v3:
>> 1) Move variables used for traversal inside the if statement;
>> 2) Add a comment to explain why we have to do this;
>> 3) Move the second check of cl_revoked inside the if statement of
>> the first check.
>> fs/nfsd/nfs4state.c | 35 +++++++++++++++++++++++++++++++++--
>> 1 file changed, 33 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 88c347957da5..20fae3449af6 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -1336,6 +1336,11 @@ static void destroy_delegation(struct nfs4_delegation *dp)
>>
>> spin_lock(&state_lock);
>> unhashed = unhash_delegation_locked(dp, SC_STATUS_CLOSED);
>> + /*
>> + * Unconditionally set SC_STATUS_CLOSED, regardless of whether the
>> + * delegation is hashed, to mark the current delegation as invalid.
>> + */
>> + dp->dl_stid.sc_status |= SC_STATUS_CLOSED;
>> spin_unlock(&state_lock);
>> if (unhashed)
>> destroy_unhashed_deleg(dp);
>> @@ -4470,8 +4475,34 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> default:
>> seq->status_flags = 0;
>> }
>> - if (!list_empty(&clp->cl_revoked))
>> - seq->status_flags |= SEQ4_STATUS_RECALLABLE_STATE_REVOKED;
>> + if (!list_empty(&clp->cl_revoked)) {
>> + struct list_head *pos, *next;
>> + struct nfs4_delegation *dp;
>> +
>> + /*
>> + * Concurrent nfs4_laundromat() and nfsd4_delegreturn()
>> + * may add a delegation to cl_revoked even after the
>> + * client has returned it, causing persistent
>> + * SEQ4_STATUS_RECALLABLE_STATE_REVOKED, disrupting normal
>> + * operations.
>> + * Remove delegations with SC_STATUS_CLOSED from cl_revoked
>> + * to resolve.
>> + */
>> + spin_lock(&clp->cl_lock);
>> + list_for_each_safe(pos, next, &clp->cl_revoked) {
>> + dp = list_entry(pos, struct nfs4_delegation, dl_recall_lru);
>> + if (dp->dl_stid.sc_status & SC_STATUS_CLOSED) {
>> + list_del_init(&dp->dl_recall_lru);
>> + spin_unlock(&clp->cl_lock);
>
> Does unlocking cl_lock here allow another CPU to free the object
> that @next is pointing to? That pointer address would then be
> dereferenced on the next loop iteration.
>
> Might be better to stuff dp onto a local list, then "put" all
> the items on that list once this loop has terminated and cl_lock
> has been released.
I intended to include this patch in nfsd-next for v6.18, but since I
haven't gotten a response, I have dropped it for now.
When we get closure on my question above, I am happy to requeue it
for a later merge window.
>> + nfs4_put_stid(&dp->dl_stid);
>> + spin_lock(&clp->cl_lock);
>> + }
>> + }
>> + spin_unlock(&clp->cl_lock);
>> +
>> + if (!list_empty(&clp->cl_revoked))
>> + seq->status_flags |= SEQ4_STATUS_RECALLABLE_STATE_REVOKED;
>> + }
>> if (atomic_read(&clp->cl_admin_revoked))
>> seq->status_flags |= SEQ4_STATUS_ADMIN_STATE_REVOKED;
>> trace_nfsd_seq4_status(rqstp, seq);
>
>
--
Chuck Lever
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