On 2/3/22 3:40 PM, Chuck Lever III wrote:
On Feb 3, 2022, at 4:38 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
On 2/3/22 11:31 AM, Chuck Lever III wrote:
On Jan 28, 2022, at 2:39 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
Currently an NFSv4 client must maintain its lease by using the at least
one of the state tokens or if nothing else, by issuing a RENEW (4.0), or
a singleton SEQUENCE (4.1) at least once during each lease period. If the
client fails to renew the lease, for any reason, the Linux server expunges
the state tokens immediately upon detection of the "failure to renew the
lease" condition and begins returning NFS4ERR_EXPIRED if the client should
reconnect and attempt to use the (now) expired state.
The default lease period for the Linux server is 90 seconds. The typical
client cuts that in half and will issue a lease renewing operation every
45 seconds. The 90 second lease period is very short considering the
potential for moderately long term network partitions. A network partition
refers to any loss of network connectivity between the NFS client and the
NFS server, regardless of its root cause. This includes NIC failures, NIC
driver bugs, network misconfigurations & administrative errors, routers &
switches crashing and/or having software updates applied, even down to
cables being physically pulled. In most cases, these network failures are
transient, although the duration is unknown.
A server which does not immediately expunge the state on lease expiration
is known as a Courteous Server. A Courteous Server continues to recognize
previously generated state tokens as valid until conflict arises between
the expired state and the requests from another client, or the server
reboots.
The initial implementation of the Courteous Server will do the following:
. When the laundromat thread detects an expired client and if that client
still has established state on the Linux server and there is no waiters
for the client's locks then deletes the client persistent record and marks
the client as COURTESY_CLIENT and skips destroying the client and all of
state, otherwise destroys the client as usual.
. Client persistent record is added to the client database when the
courtesy client reconnects and transits to normal client.
. Lock/delegation/share reversation conflict with courtesy client is
resolved by marking the courtesy client as DESTROY_COURTESY_CLIENT,
effectively disable it, then allow the current request to proceed
immediately.
. Courtesy client marked as DESTROY_COURTESY_CLIENT is not allowed to
reconnect to reuse itsstate. It is expired by the laundromat asynchronously
in the background.
Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
---
fs/nfsd/nfs4state.c | 454 +++++++++++++++++++++++++++++++++++++++++++++++-----
fs/nfsd/state.h | 5 +
2 files changed, 415 insertions(+), 44 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 1956d377d1a6..b302d857e196 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1913,14 +1915,37 @@ __find_in_sessionid_hashtbl(struct nfs4_sessionid *sessionid, struct net *net)
static struct nfsd4_session *
find_in_sessionid_hashtbl(struct nfs4_sessionid *sessionid, struct net *net,
- __be32 *ret)
+ __be32 *ret, bool *courtesy_clnt)
IMO the new @courtesy_clnt parameter isn't necessary.
Just create a new cl_flag:
+#define NFSD4_COURTESY_CLIENT (6) /* be nice to expired client */
+#define NFSD4_DESTROY_COURTESY_CLIENT (7)
#define NFSD4_CLIENT_PROMOTE_COURTESY (8)
or REHYDRATE_COURTESY some such.
Set that flag and check it once it is safe to call
nfsd4_client_record_create().
We need the 'courtesy_clnt' parameter so caller can specify
whether the courtesy client should be promoted or not.
I understand what the flag is used for in the patch, but I
prefer to see this implemented without changing the synopsis
of all those functions. Especially adding an output parameter
like this is usually frowned upon.
The struct nfs_client can carry this flag, if not in cl_flags,
then perhaps in another field. That struct is visible in every
one of the callers.
The struct nfs4_client is not available to the caller of
find_in_sessionid_hashtbl at the time it calls the function and
the current input parameters of find_in_sessionid_hashtbl can
not be used to specify this flag.
-Dai
--
Chuck Lever
