CIFS: Introduce credit-based flow control

and send no more than credits value requests at once. For SMB/CIFS
it's trivial: increment this value by receiving any message and
decrement by sending one.

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>

6 files changed, 60 insertions, 44 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index fb78bc903887..d55de9684df9 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -250,8 +250,9 @@ struct TCP_Server_Info {
         bool noblocksnd;                /* use blocking sendmsg */
         bool noautotune;                /* do not autotune send buf sizes */
         bool tcp_nodelay;
+        int credits;  /* send no more requests at once */
         unsigned int in_flight;  /* number of requests on the wire to server */
-        spinlock_t req_lock; /* protect the value above */
+        spinlock_t req_lock;  /* protect the two values above */
         struct mutex srv_mutex;
         struct task_struct *tsk;
         char server_GUID[16];
@@ -314,12 +315,14 @@ in_flight(struct TCP_Server_Info *server)
         return num;
 }
 
-static inline void
-dec_in_flight(struct TCP_Server_Info *server)
+static inline bool
+has_credits(struct TCP_Server_Info *server)
 {
+        int num;
         spin_lock(&server->req_lock);
-        server->in_flight--;
+        num = server->credits;
         spin_unlock(&server->req_lock);
+        return num > 0;
 }
 
 /*
diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 6f4e243e0f62..47a769e535b1 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -88,6 +88,9 @@ extern int SendReceiveBlockingLock(const unsigned int xid,
                         struct smb_hdr *in_buf ,
                         struct smb_hdr *out_buf,
                         int *bytes_returned);
+extern void cifs_add_credits(struct TCP_Server_Info *server,
+                             const unsigned int add);
+extern void cifs_set_credits(struct TCP_Server_Info *server, const int val);
 extern int checkSMB(struct smb_hdr *smb, __u16 mid, unsigned int length);
 extern bool is_valid_oplock_break(struct smb_hdr *smb,
                                   struct TCP_Server_Info *);
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index d7cbcfa21a0c..70aac35c398f 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -461,7 +461,7 @@ CIFSSMBNegotiate(unsigned int xid, struct cifs_ses *ses)
                 server->maxReq = min_t(unsigned int,
                                        le16_to_cpu(rsp->MaxMpxCount),
                                        cifs_max_pending);
-                server->oplocks = server->maxReq > 1 ? enable_oplocks : false;
+                cifs_set_credits(server, server->maxReq);
                 server->maxBuf = le16_to_cpu(rsp->MaxBufSize);
                 server->max_vcs = le16_to_cpu(rsp->MaxNumberVcs);
                 /* even though we do not use raw we might as well set this
@@ -569,7 +569,7 @@ CIFSSMBNegotiate(unsigned int xid, struct cifs_ses *ses)
            little endian */
         server->maxReq = min_t(unsigned int, le16_to_cpu(pSMBr->MaxMpxCount),
                                cifs_max_pending);
-        server->oplocks = server->maxReq > 1 ? enable_oplocks : false;
+        cifs_set_credits(server, server->maxReq);
         /* probably no need to store and check maxvcs */
         server->maxBuf = le32_to_cpu(pSMBr->MaxBufferSize);
         server->max_rw = le32_to_cpu(pSMBr->MaxRawSize);
@@ -721,8 +721,7 @@ cifs_echo_callback(struct mid_q_entry *mid)
         struct TCP_Server_Info *server = mid->callback_data;
 
         DeleteMidQEntry(mid);
-        dec_in_flight(server);
-        wake_up(&server->request_q);
+        cifs_add_credits(server, 1);
 }
 
 int
@@ -1674,8 +1673,7 @@ cifs_readv_callback(struct mid_q_entry *mid)
 
         queue_work(system_nrt_wq, &rdata->work);
         DeleteMidQEntry(mid);
-        dec_in_flight(server);
-        wake_up(&server->request_q);
+        cifs_add_credits(server, 1);
 }
 
 /* cifs_async_readv - send an async write, and set up mid to handle result */
@@ -2115,8 +2113,7 @@ cifs_writev_callback(struct mid_q_entry *mid)
 
         queue_work(system_nrt_wq, &wdata->work);
         DeleteMidQEntry(mid);
-        dec_in_flight(tcon->ses->server);
-        wake_up(&tcon->ses->server->request_q);
+        cifs_add_credits(tcon->ses->server, 1);
 }
 
 /* cifs_async_writev - send an async write, and set up mid to handle result */
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index ed91abcce8a9..1d489010615b 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -642,14 +642,10 @@ static void clean_demultiplex_info(struct TCP_Server_Info *server)
         spin_unlock(&GlobalMid_Lock);
         wake_up_all(&server->response_q);
 
-        /* Check if we have blocked requests that need to free. */
+        /* check if we have blocked requests that need to free */
         spin_lock(&server->req_lock);
-        if (server->in_flight >= server->maxReq)
-                server->in_flight = server->maxReq - 1;
-        /*
-         * We do not want to set the max_pending too low or we could end up
-         * with the counter going negative.
-         */
+        if (server->credits <= 0)
+                server->credits = 1;
         spin_unlock(&server->req_lock);
         /*
          * Although there should not be any requests blocked on this queue it
@@ -1906,7 +1902,7 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
         tcp_ses->noautotune = volume_info->noautotune;
         tcp_ses->tcp_nodelay = volume_info->sockopt_tcp_nodelay;
         tcp_ses->in_flight = 0;
-        tcp_ses->maxReq = 1; /* enough to send negotiate request */
+        tcp_ses->credits = 1;
         init_waitqueue_head(&tcp_ses->response_q);
         init_waitqueue_head(&tcp_ses->request_q);
         INIT_LIST_HEAD(&tcp_ses->pending_mid_q);
@@ -3757,9 +3753,11 @@ int cifs_negotiate_protocol(unsigned int xid, struct cifs_ses *ses)
         if (server->maxBuf != 0)
                 return 0;
 
+        cifs_set_credits(server, 1);
         rc = CIFSSMBNegotiate(xid, ses);
         if (rc == -EAGAIN) {
                 /* retry only once on 1st time connection */
+                cifs_set_credits(server, 1);
                 rc = CIFSSMBNegotiate(xid, ses);
                 if (rc == -EAGAIN)
                         rc = -EHOSTDOWN;
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 703ef5c6fdb1..c273c12de98e 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -690,3 +690,22 @@ backup_cred(struct cifs_sb_info *cifs_sb)
 
         return false;
 }
+
+void
+cifs_add_credits(struct TCP_Server_Info *server, const unsigned int add)
+{
+        spin_lock(&server->req_lock);
+        server->credits += add;
+        server->in_flight--;
+        spin_unlock(&server->req_lock);
+        wake_up(&server->request_q);
+}
+
+void
+cifs_set_credits(struct TCP_Server_Info *server, const int val)
+{
+        spin_lock(&server->req_lock);
+        server->credits = val;
+        server->oplocks = val > 1 ? enable_oplocks : false;
+        spin_unlock(&server->req_lock);
+}
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index e2673aa34381..e5202ddef2fb 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -262,16 +262,16 @@ wait_for_free_request(struct TCP_Server_Info *server, const int long_op)
         if (long_op == CIFS_ASYNC_OP) {
                 /* oplock breaks must not be held up */
                 server->in_flight++;
+                server->credits--;
                 spin_unlock(&server->req_lock);
                 return 0;
         }
 
         while (1) {
-                if (server->in_flight >= server->maxReq) {
+                if (server->credits <= 0) {
                         spin_unlock(&server->req_lock);
                         cifs_num_waiters_inc(server);
-                        wait_event(server->request_q,
-                                   in_flight(server) < server->maxReq);
+                        wait_event(server->request_q, has_credits(server));
                         cifs_num_waiters_dec(server);
                         spin_lock(&server->req_lock);
                 } else {
@@ -280,12 +280,16 @@ wait_for_free_request(struct TCP_Server_Info *server, const int long_op)
                                 return -ENOENT;
                         }
 
-                        /* can not count locking commands against total
-                           as they are allowed to block on server */
+                        /*
+                         * Can not count locking commands against total
+                         * as they are allowed to block on server.
+                         */
 
                         /* update # of requests on the wire to server */
-                        if (long_op != CIFS_BLOCKING_OP)
+                        if (long_op != CIFS_BLOCKING_OP) {
+                                server->credits--;
                                 server->in_flight++;
+                        }
                         spin_unlock(&server->req_lock);
                         break;
                 }
@@ -360,7 +364,7 @@ cifs_call_async(struct TCP_Server_Info *server, struct kvec *iov,
         mid = AllocMidQEntry(hdr, server);
         if (mid == NULL) {
                 mutex_unlock(&server->srv_mutex);
-                dec_in_flight(server);
+                cifs_add_credits(server, 1);
                 wake_up(&server->request_q);
                 return -ENOMEM;
         }
@@ -393,7 +397,7 @@ cifs_call_async(struct TCP_Server_Info *server, struct kvec *iov,
         return rc;
 out_err:
         delete_mid(mid);
-        dec_in_flight(server);
+        cifs_add_credits(server, 1);
         wake_up(&server->request_q);
         return rc;
 }
@@ -565,8 +569,7 @@ SendReceive2(const unsigned int xid, struct cifs_ses *ses,
                 mutex_unlock(&ses->server->srv_mutex);
                 cifs_small_buf_release(in_buf);
                 /* Update # of requests on wire to server */
-                dec_in_flight(ses->server);
-                wake_up(&ses->server->request_q);
+                cifs_add_credits(ses->server, 1);
                 return rc;
         }
         rc = cifs_sign_smb2(iov, n_vec, ses->server, &midQ->sequence_number);
@@ -602,8 +605,7 @@ SendReceive2(const unsigned int xid, struct cifs_ses *ses,
                         midQ->callback = DeleteMidQEntry;
                         spin_unlock(&GlobalMid_Lock);
                         cifs_small_buf_release(in_buf);
-                        dec_in_flight(ses->server);
-                        wake_up(&ses->server->request_q);
+                        cifs_add_credits(ses->server, 1);
                         return rc;
                 }
                 spin_unlock(&GlobalMid_Lock);
@@ -613,8 +615,7 @@ SendReceive2(const unsigned int xid, struct cifs_ses *ses,
 
         rc = cifs_sync_mid_result(midQ, ses->server);
         if (rc != 0) {
-                dec_in_flight(ses->server);
-                wake_up(&ses->server->request_q);
+                cifs_add_credits(ses->server, 1);
                 return rc;
         }
 
@@ -638,8 +639,7 @@ SendReceive2(const unsigned int xid, struct cifs_ses *ses,
                 midQ->resp_buf = NULL;
 out:
         delete_mid(midQ);
-        dec_in_flight(ses->server);
-        wake_up(&ses->server->request_q);
+        cifs_add_credits(ses->server, 1);
 
         return rc;
 }
@@ -689,8 +689,7 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
         if (rc) {
                 mutex_unlock(&ses->server->srv_mutex);
                 /* Update # of requests on wire to server */
-                dec_in_flight(ses->server);
-                wake_up(&ses->server->request_q);
+                cifs_add_credits(ses->server, 1);
                 return rc;
         }
 
@@ -722,8 +721,7 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
                         /* no longer considered to be "in-flight" */
                         midQ->callback = DeleteMidQEntry;
                         spin_unlock(&GlobalMid_Lock);
-                        dec_in_flight(ses->server);
-                        wake_up(&ses->server->request_q);
+                        cifs_add_credits(ses->server, 1);
                         return rc;
                 }
                 spin_unlock(&GlobalMid_Lock);
@@ -731,8 +729,7 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
 
         rc = cifs_sync_mid_result(midQ, ses->server);
         if (rc != 0) {
-                dec_in_flight(ses->server);
-                wake_up(&ses->server->request_q);
+                cifs_add_credits(ses->server, 1);
                 return rc;
         }
 
@@ -748,8 +745,7 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
         rc = cifs_check_receive(midQ, ses->server, 0);
 out:
         delete_mid(midQ);
-        dec_in_flight(ses->server);
-        wake_up(&ses->server->request_q);
+        cifs_add_credits(ses->server, 1);
 
         return rc;
 }