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authorRonnie Sahlberg <lsahlber@redhat.com>2019-03-08 12:58:21 +1000
committerSteve French <stfrench@microsoft.com>2019-03-14 19:32:35 -0500
commit16b34aa44b257155d9392a19e08e4ce139bc2789 (patch)
treea82a838ff7d699fe399913d393e9544b51b25c29 /fs/cifs
parentb227d215deef4f3528b8f754accef4db03539a59 (diff)
cifs: prevent starvation in wait_for_free_credits for multi-credit requests
Reserve the last MAX_COMPOUND credits for any request asking for >1 credit. This is to prevent future compound requests from becoming starved while waiting for potentially many requests is there is a large number of concurrent singe-credit requests. However, we need to protect from servers that are very slow to hand out new credits on new sessions so we only do this IFF there are 2*MAX_COMPOUND (arbitrary) credits already in flight. Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> Signed-off-by: Steve French <stfrench@microsoft.com> Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Diffstat (limited to 'fs/cifs')
-rw-r--r--fs/cifs/transport.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 1951f9f74bb2..9e08ce722dbb 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -529,6 +529,34 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
}
/*
+ * For normal commands, reserve the last MAX_COMPOUND
+ * credits to compound requests.
+ * Otherwise these compounds could be permanently
+ * starved for credits by single-credit requests.
+ *
+ * To prevent spinning CPU, block this thread until
+ * there are >MAX_COMPOUND credits available.
+ * But only do this is we already have a lot of
+ * credits in flight to avoid triggering this check
+ * for servers that are slow to hand out credits on
+ * new sessions.
+ */
+ if (!optype && num_credits == 1 &&
+ server->in_flight > 2 * MAX_COMPOUND &&
+ *credits <= MAX_COMPOUND) {
+ spin_unlock(&server->req_lock);
+ cifs_num_waiters_inc(server);
+ rc = wait_event_killable(server->request_q,
+ has_credits(server, credits,
+ MAX_COMPOUND + 1));
+ cifs_num_waiters_dec(server);
+ if (rc)
+ return rc;
+ spin_lock(&server->req_lock);
+ continue;
+ }
+
+ /*
* Can not count locking commands against total
* as they are allowed to block on server.
*/