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Commit 2b6e72ed authored by Dominique Martinet's avatar Dominique Martinet Committed by Eric Van Hensbergen
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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: default avatarDominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: default avatarEric Van Hensbergen <ericvh@gmail.com>
parent 38dbfb59

include/net/9p/client.h

+1 −1
Original line number Diff line number Diff line
@@ -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 *);

net/9p/client.c

+15 −1
Original line number Diff line number Diff line
@@ -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 @@ p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...) 
	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;

net/9p/trans_fd.c

+6 −9
Original line number Diff line number Diff line
@@ -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;

net/9p/trans_rdma.c

+1 −2
Original line number Diff line number Diff line
@@ -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;

net/9p/trans_virtio.c

+1 −2
Original line number Diff line number Diff line
@@ -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);

	}

}