On Fri, Aug 18 2017, Trond Myklebust wrote:
> On Fri, 2017-08-18 at 17:12 +1000, NeilBrown wrote:
>> If you try an NFSv4 mount from an inaccessible server, it will hang
>> as
>> you would expect.
>> If you then try an NFSv4 mount from a different accessible server,
>> it will also hang. This is not expected.
>>
>> The second mount is blocked in
>> nfs4_init_client()
>> -> nfs4_discover_server_trunking()
>> -> nfs40_discover_server_trunking()
>> -> nfs40_walk_client_list()
>> -> nfs4_match_client()
>> -> nfs_wait_client_init_complete()
>> It is waiting for the first mount to complete so that it can then
>> see if the two servers are really one and the same.
>>
>> It is not necessary to wait here when an nfs_client cl_cons_state is
>> NFS_CS_INITING. Such a client will, after changing cl_cons_state,
>> call
>> nfs4_discover_server_trunking() itself. So if the current client
>> just
>> skips those clients, trunking will still be discovered if necessary.
>>
>> I am unsure of situation with NFS_CS_SESSION_INITING, but I suspect
>> that the comment "Wait for CREATE_SESSION to finish" implies that
>> it is only clients in NFS_CS_SESSION_INITING that need to be waited
>> for.
>>
>> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
>> ---
>> fs/nfs/nfs4client.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
>> index e9bea90dc017..d8b9b7ff19a9 100644
>> --- a/fs/nfs/nfs4client.c
>> +++ b/fs/nfs/nfs4client.c
>> @@ -482,7 +482,7 @@ static int nfs4_match_client(struct
>> nfs_client *pos, struct nfs_client *new,
>> * remaining fields in "pos", especially the client
>> * ID and serverowner fields. Wait for CREATE_SESSION
>> * to finish. */
>> - if (pos->cl_cons_state > NFS_CS_READY) {
>> + if (pos->cl_cons_state == NFS_CS_SESSION_INITING) {
>> atomic_inc(&pos->cl_count);
>> spin_unlock(&nn->nfs_client_lock);
>
> This could cause us to declare a false positive match with a client
> that is uninitialised.
Thanks for the review.
A positive match is reported by returning zero.
If cl_cons_state is not NFS_CS_READY, nfs4_match_client() will not
return zero.
So I don't see how a false positive is possible.
A false negative might be possible with an uninitialized client, but
once that client is initialised, it will call walk_client_list and find
the match. Won't it?
Thanks,
NeilBrown
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