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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>
This commit is contained in:
Dominique Martinet 2014-01-17 18:31:00 +01:00 committed by Eric Van Hensbergen
parent 38dbfb59d1
commit 2b6e72ed74
5 changed files with 24 additions and 15 deletions
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2
include/net/9p/client.h
View File

@ -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 *);

16
net/9p/client.c
View File

@ -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;

15
net/9p/trans_fd.c
View File

@ -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;

3
net/9p/trans_rdma.c
View File

@ -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;

3
net/9p/trans_virtio.c
View File

@ -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);
}
}