forked from Minki/linux
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: Trond Myklebust <trond.myklebust@primarydata.com>
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0d2a970d0a
@ -212,7 +212,8 @@ struct rpc_xprt {
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#if defined(CONFIG_SUNRPC_BACKCHANNEL)
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struct svc_serv *bc_serv; /* The RPC service which will */
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/* process the callback */
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unsigned int bc_alloc_count; /* Total number of preallocs */
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int bc_alloc_count; /* Total number of preallocs */
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atomic_t bc_free_slots;
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spinlock_t bc_pa_lock; /* Protects the preallocated
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* items */
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struct list_head bc_pa_list; /* List of preallocated
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@ -37,16 +37,18 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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static inline int xprt_need_to_requeue(struct rpc_xprt *xprt)
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{
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return xprt->bc_alloc_count > 0;
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return xprt->bc_alloc_count < atomic_read(&xprt->bc_free_slots);
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}
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static inline void xprt_inc_alloc_count(struct rpc_xprt *xprt, unsigned int n)
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{
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atomic_add(n, &xprt->bc_free_slots);
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xprt->bc_alloc_count += n;
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}
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static inline int xprt_dec_alloc_count(struct rpc_xprt *xprt, unsigned int n)
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{
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atomic_sub(n, &xprt->bc_free_slots);
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return xprt->bc_alloc_count -= n;
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}
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@ -232,9 +234,15 @@ static struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt, __be32 xid)
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struct rpc_rqst *req = NULL;
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dprintk("RPC: allocate a backchannel request\n");
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if (list_empty(&xprt->bc_pa_list))
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if (atomic_read(&xprt->bc_free_slots) <= 0)
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goto not_found;
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if (list_empty(&xprt->bc_pa_list)) {
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req = xprt_alloc_bc_req(xprt, GFP_ATOMIC);
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if (!req)
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goto not_found;
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/* Note: this 'free' request adds it to xprt->bc_pa_list */
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xprt_free_bc_request(req);
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}
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req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
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rq_bc_pa_list);
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req->rq_reply_bytes_recvd = 0;
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@ -260,11 +268,21 @@ void xprt_free_bc_request(struct rpc_rqst *req)
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req->rq_connect_cookie = xprt->connect_cookie - 1;
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smp_mb__before_atomic();
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WARN_ON_ONCE(!test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));
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clear_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
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smp_mb__after_atomic();
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if (!xprt_need_to_requeue(xprt)) {
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/*
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* Return it to the list of preallocations so that it
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* may be reused by a new callback request.
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*/
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spin_lock_bh(&xprt->bc_pa_lock);
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if (xprt_need_to_requeue(xprt)) {
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list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
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xprt->bc_alloc_count++;
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req = NULL;
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}
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spin_unlock_bh(&xprt->bc_pa_lock);
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if (req != NULL) {
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/*
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* The last remaining session was destroyed while this
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* entry was in use. Free the entry and don't attempt
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@ -275,14 +293,6 @@ void xprt_free_bc_request(struct rpc_rqst *req)
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xprt_free_allocation(req);
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return;
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}
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/*
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* Return it to the list of preallocations so that it
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* may be reused by a new callback request.
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*/
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spin_lock_bh(&xprt->bc_pa_lock);
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list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
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spin_unlock_bh(&xprt->bc_pa_lock);
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}
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/*
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@ -326,6 +336,7 @@ void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
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spin_lock(&xprt->bc_pa_lock);
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list_del(&req->rq_bc_pa_list);
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xprt->bc_alloc_count--;
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spin_unlock(&xprt->bc_pa_lock);
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req->rq_private_buf.len = copied;
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@ -1351,6 +1351,7 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
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struct kvec *argv = &rqstp->rq_arg.head[0];
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struct kvec *resv = &rqstp->rq_res.head[0];
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struct rpc_task *task;
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int proc_error;
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int error;
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dprintk("svc: %s(%p)\n", __func__, req);
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@ -1382,7 +1383,10 @@ bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
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svc_getnl(argv); /* CALLDIR */
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/* Parse and execute the bc call */
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if (!svc_process_common(rqstp, argv, resv)) {
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proc_error = svc_process_common(rqstp, argv, resv);
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atomic_inc(&req->rq_xprt->bc_free_slots);
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if (!proc_error) {
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/* Processing error: drop the request */
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xprt_free_bc_request(req);
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return 0;
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