Commit 0d2a970d authored by Trond Myklebust's avatar Trond Myklebust
Browse files

SUNRPC: Fix a backchannel race 



We need to allow the server to send a new request immediately after we've
replied to the previous one. Right now, there is a window between the
send and the release of the old request in rpc_put_task(), where the
server could send us a new backchannel RPC call, and we have no
request to service it.

Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
parent 1dddda86

include/linux/sunrpc/xprt.h

+2 −1
Original line number Diff line number Diff line
@@ -212,7 +212,8 @@ struct rpc_xprt { 
#if defined(CONFIG_SUNRPC_BACKCHANNEL)

	struct svc_serv		*bc_serv;       /* The RPC service which will */

						/* process the callback */

	unsigned int		bc_alloc_count;	/* Total number of preallocs */

	int			bc_alloc_count;	/* Total number of preallocs */

	atomic_t		bc_free_slots;

	spinlock_t		bc_pa_lock;	/* Protects the preallocated

						 * items */

	struct list_head	bc_pa_list;	/* List of preallocated

net/sunrpc/backchannel_rqst.c

+24 −13
Original line number Diff line number Diff line
@@ -37,16 +37,18 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

static inline int xprt_need_to_requeue(struct rpc_xprt *xprt)

{

	return xprt->bc_alloc_count > 0;

	return xprt->bc_alloc_count < atomic_read(&xprt->bc_free_slots);

}



static inline void xprt_inc_alloc_count(struct rpc_xprt *xprt, unsigned int n)

{

	atomic_add(n, &xprt->bc_free_slots);

	xprt->bc_alloc_count += n;

}



static inline int xprt_dec_alloc_count(struct rpc_xprt *xprt, unsigned int n)

{

	atomic_sub(n, &xprt->bc_free_slots);

	return xprt->bc_alloc_count -= n;

}
@@ -232,9 +234,15 @@ static struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt, __be32 xid) 
	struct rpc_rqst *req = NULL;



	dprintk("RPC:       allocate a backchannel request\n");

	if (list_empty(&xprt->bc_pa_list))

	if (atomic_read(&xprt->bc_free_slots) <= 0)

		goto not_found;



	if (list_empty(&xprt->bc_pa_list)) {

		req = xprt_alloc_bc_req(xprt, GFP_ATOMIC);

		if (!req)

			goto not_found;

		/* Note: this 'free' request adds it to xprt->bc_pa_list */

		xprt_free_bc_request(req);

	}

	req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,

				rq_bc_pa_list);

	req->rq_reply_bytes_recvd = 0;
@@ -260,11 +268,21 @@ void xprt_free_bc_request(struct rpc_rqst *req) 


	req->rq_connect_cookie = xprt->connect_cookie - 1;

	smp_mb__before_atomic();

	WARN_ON_ONCE(!test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));

	clear_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);

	smp_mb__after_atomic();



	if (!xprt_need_to_requeue(xprt)) {

	/*

	 * Return it to the list of preallocations so that it

	 * may be reused by a new callback request.

	 */

	spin_lock_bh(&xprt->bc_pa_lock);

	if (xprt_need_to_requeue(xprt)) {

		list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);

		xprt->bc_alloc_count++;

		req = NULL;

	}

	spin_unlock_bh(&xprt->bc_pa_lock);

	if (req != NULL) {

		/*

		 * The last remaining session was destroyed while this

		 * entry was in use.  Free the entry and don't attempt
@@ -275,14 +293,6 @@ void xprt_free_bc_request(struct rpc_rqst *req) 
		xprt_free_allocation(req);

		return;

	}



	/*

	 * Return it to the list of preallocations so that it

	 * may be reused by a new callback request.

	 */

	spin_lock_bh(&xprt->bc_pa_lock);

	list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);

	spin_unlock_bh(&xprt->bc_pa_lock);

}



/*
@@ -326,6 +336,7 @@ void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied) 


	spin_lock(&xprt->bc_pa_lock);

	list_del(&req->rq_bc_pa_list);

	xprt->bc_alloc_count--;

	spin_unlock(&xprt->bc_pa_lock);



	req->rq_private_buf.len = copied;

net/sunrpc/svc.c

+5 −1
Original line number Diff line number Diff line
@@ -1351,6 +1351,7 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req, 
	struct kvec	*argv = &rqstp->rq_arg.head[0];

	struct kvec	*resv = &rqstp->rq_res.head[0];

	struct rpc_task *task;

	int proc_error;

	int error;



	dprintk("svc: %s(%p)\n", __func__, req);
@@ -1382,7 +1383,10 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req, 
	svc_getnl(argv);	/* CALLDIR */



	/* Parse and execute the bc call */

	if (!svc_process_common(rqstp, argv, resv)) {

	proc_error = svc_process_common(rqstp, argv, resv);



	atomic_inc(&req->rq_xprt->bc_free_slots);

	if (!proc_error) {

		/* Processing error: drop the request */

		xprt_free_bc_request(req);

		return 0;

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