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Handle resent initial client greetings

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The very first greeting a client sends is unique becuase it doesn't yet
have a server_term field set and tells the server to create items to
track the client.

A server processing this request can create the items and then shut down
before the client is able to receive the reply.  They'll resend the
greeting without server_term but then the next server will get -EEXIST
errors as it tries to create items for the client.  This causes the
connection to break, which the client tries to reestablish, and the
pattern repeats indefinitely.

The fix is to simply recognize that -EEXIST is acceptable during item
creation.  Server message handlers always have to address the case where
a resent message was already processed by a previous server but it's
response didn't make it to the client.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2021-03-16 11:52:18 -07:00
parent 73084462e9
commit 7d67489b0c
2 changed files with 13 additions and 1 deletions
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6
kmod/src/lock_server.c
View File

@@ -586,7 +586,9 @@ static void init_lock_clients_key(struct scoutfs_key *key, u64 rid)
* the client had already talked to the server then we must find an
* existing record for it and should begin recovery. If it doesn't have
* a record then its timed out and we can't allow it to reconnect. If
* its connecting for the first time then we insert a new record. If
* we're creating a new record for a client we can see EEXIST if the
* greeting is resent to a new server after the record was committed but
* before the response was received by the client.
*
* This is running in concurrent client greeting processing contexts.
*/
@@ -611,6 +613,8 @@ int scoutfs_lock_server_greeting(struct super_block *sb, u64 rid,
ret = scoutfs_btree_insert(sb, inf->alloc, inf->wri,
&super->lock_clients,
&key, NULL, 0);
if (ret == -EEXIST)
ret = 0;
}
mutex_unlock(&inf->mutex);

8
kmod/src/server.c
View File

@@ -1024,6 +1024,12 @@ static void init_mounted_client_key(struct scoutfs_key *key, u64 rid)
};
}
/*
* Insert a new mounted client item for a client that is sending us a
* greeting that hasn't yet seen a response. The greeting can be
* retransmitted to a new server after the previous inserted the item so
* it's acceptable to see -EEXIST.
*/
static int insert_mounted_client(struct super_block *sb, u64 rid,
u64 gr_flags)
{
@@ -1042,6 +1048,8 @@ static int insert_mounted_client(struct super_block *sb, u64 rid,
ret = scoutfs_btree_insert(sb, &server->alloc, &server->wri,
&super->mounted_clients, &key, &mcv,
sizeof(mcv));
if (ret == -EEXIST)
ret = 0;
mutex_unlock(&server->mounted_clients_mutex);
return ret;