9P: Add memory barriers to protect request fields over cb/rpc threads handoff

We need barriers to guarantee this pattern works as intended:
[w] req->rc, 1		[r] req->status, 1
wmb			rmb
[w] req->status, 1	[r] req->rc

Where the wmb ensures that rc gets written before status,
and the rmb ensures that if you observe status == 1, rc is the new value.

Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

diff --git a/include/net/9p/client.h b/include/net/9p/client.h
index c38a005bd0cf9d84a09216cd6f47102e71bb2972..115aeac401b187d9016530f3a9d996697d7b4e2a 100644 (file)
--- a/include/net/9p/client.h
+++ b/include/net/9p/client.h
@@ -261,7 +261,7 @@ int p9_client_mkdir_dotl(struct p9_fid *fid, char *name, int mode,
 int p9_client_lock_dotl(struct p9_fid *fid, struct p9_flock *flock, u8 *status);
 int p9_client_getlock_dotl(struct p9_fid *fid, struct p9_getlock *fl);
 struct p9_req_t *p9_tag_lookup(struct p9_client *, u16);
-void p9_client_cb(struct p9_client *c, struct p9_req_t *req);
+void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status);
 
 int p9_parse_header(struct p9_fcall *, int32_t *, int8_t *, int16_t *, int);
 int p9stat_read(struct p9_client *, char *, int, struct p9_wstat *);

diff --git a/net/9p/client.c b/net/9p/client.c
index a5e4d2dcb03e8c98eae243e1dd1b82cea68bd227..95b1836173e1348510ad201fd01e53031a33d0b5 100644 (file)
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -415,9 +415,17 @@ static void p9_free_req(struct p9_client *c, struct p9_req_t *r)
  * req: request received
  *
  */
-void p9_client_cb(struct p9_client *c, struct p9_req_t *req)
+void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status)
 {
        p9_debug(P9_DEBUG_MUX, " tag %d\n", req->tc->tag);
+
+       /*
+        * This barrier is needed to make sure any change made to req before
+        * the other thread wakes up will indeed be seen by the waiting side.
+        */
+       smp_wmb();
+       req->status = status;
+
        wake_up(req->wq);
        p9_debug(P9_DEBUG_MUX, "wakeup: %d\n", req->tc->tag);
 }
@@ -751,6 +759,12 @@ again:
        err = wait_event_interruptible(*req->wq,
                                       req->status >= REQ_STATUS_RCVD);
 
+       /*
+        * Make sure our req is coherent with regard to updates in other
+        * threads - echoes to wmb() in the callback
+        */
+       smp_rmb();
+
        if ((err == -ERESTARTSYS) && (c->status == Connected)
                                  && (type == P9_TFLUSH)) {
                sigpending = 1;

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index b7bd7f2961bf60f49258bd60a702eadd8d651773..193efd5624661842e18eae7d9d0a12ff2c9d6b73 100644 (file)
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -212,15 +212,9 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
        m->err = err;
 
        list_for_each_entry_safe(req, rtmp, &m->req_list, req_list) {
-               req->status = REQ_STATUS_ERROR;
-               if (!req->t_err)
-                       req->t_err = err;
                list_move(&req->req_list, &cancel_list);
        }
        list_for_each_entry_safe(req, rtmp, &m->unsent_req_list, req_list) {
-               req->status = REQ_STATUS_ERROR;
-               if (!req->t_err)
-                       req->t_err = err;
                list_move(&req->req_list, &cancel_list);
        }
        spin_unlock_irqrestore(&m->client->lock, flags);
@@ -228,7 +222,9 @@ static void p9_conn_cancel(struct p9_conn *m, int err)
        list_for_each_entry_safe(req, rtmp, &cancel_list, req_list) {
                p9_debug(P9_DEBUG_ERROR, "call back req %p\n", req);
                list_del(&req->req_list);
-               p9_client_cb(m->client, req);
+               if (!req->t_err)
+                       req->t_err = err;
+               p9_client_cb(m->client, req, REQ_STATUS_ERROR);
        }
 }
 
@@ -302,6 +298,7 @@ static void p9_read_work(struct work_struct *work)
 {
        int n, err;
        struct p9_conn *m;
+       int status = REQ_STATUS_ERROR;
 
        m = container_of(work, struct p9_conn, rq);
 
@@ -375,10 +372,10 @@ static void p9_read_work(struct work_struct *work)
                p9_debug(P9_DEBUG_TRANS, "got new packet\n");
                spin_lock(&m->client->lock);
                if (m->req->status != REQ_STATUS_ERROR)
-                       m->req->status = REQ_STATUS_RCVD;
+                       status = REQ_STATUS_RCVD;
                list_del(&m->req->req_list);
                spin_unlock(&m->client->lock);
-               p9_client_cb(m->client, m->req);
+               p9_client_cb(m->client, m->req, status);
                m->rbuf = NULL;
                m->rpos = 0;
                m->rsize = 0;

diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
index 8f68df5d29731cf23b6de1bbee5284c904006c93..f127ae5049111b11ca8d28f22a75c26ed4718885 100644 (file)
--- a/net/9p/trans_rdma.c
+++ b/net/9p/trans_rdma.c
@@ -305,8 +305,7 @@ handle_recv(struct p9_client *client, struct p9_trans_rdma *rdma,
        }
 
        req->rc = c->rc;
-       req->status = REQ_STATUS_RCVD;
-       p9_client_cb(client, req);
+       p9_client_cb(client, req, REQ_STATUS_RCVD);
 
        return;
 

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index cd1e1ede73a45c2516091263c937f45024616c4e..a8c67e2be3f8868a9a3d4414345a3a2d5702f0cd 100644 (file)
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -164,8 +164,7 @@ static void req_done(struct virtqueue *vq)
                p9_debug(P9_DEBUG_TRANS, ": rc %p\n", rc);
                p9_debug(P9_DEBUG_TRANS, ": lookup tag %d\n", rc->tag);
                req = p9_tag_lookup(chan->client, rc->tag);
-               req->status = REQ_STATUS_RCVD;
-               p9_client_cb(chan->client, req);
+               p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
        }
 }