diff options
| author | Ronnie Sahlberg <lsahlber@redhat.com> | 2019-03-08 05:58:21 +0300 |
|---|---|---|
| committer | Steve French <stfrench@microsoft.com> | 2019-03-15 03:32:35 +0300 |
| commit | 16b34aa44b257155d9392a19e08e4ce139bc2789 (patch) | |
| tree | a82a838ff7d699fe399913d393e9544b51b25c29 | |
| parent | b227d215deef4f3528b8f754accef4db03539a59 (diff) | |
| download | linux-16b34aa44b257155d9392a19e08e4ce139bc2789.tar.xz | |
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>
| -rw-r--r-- | fs/cifs/transport.c | 28 |
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. */ |