rxrpc: Impose a maximum number of client calls

Impose a maximum on the number of client rxrpc calls that are allowed
simultaneously.  This will be in lieu of a maximum number of client
connections as this is easier to administed as, unlike connections, calls
aren't reusable (to be changed in a subsequent patch)..

This doesn't affect the limits on service calls and connections.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index a40fae013942..c8015c76a81c 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -41,6 +41,11 @@ const char *const rxrpc_call_completions[NR__RXRPC_CALL_COMPLETIONS] = {
 
 struct kmem_cache *rxrpc_call_jar;
 
+static struct semaphore rxrpc_call_limiter =
+	__SEMAPHORE_INITIALIZER(rxrpc_call_limiter, 1000);
+static struct semaphore rxrpc_kernel_call_limiter =
+	__SEMAPHORE_INITIALIZER(rxrpc_kernel_call_limiter, 1000);
+
 static void rxrpc_call_timer_expired(struct timer_list *t)
 {
 	struct rxrpc_call *call = from_timer(call, t, timer);
@@ -210,6 +215,34 @@ static void rxrpc_start_call_timer(struct rxrpc_call *call)
 }
 
 /*
+ * Wait for a call slot to become available.
+ */
+static struct semaphore *rxrpc_get_call_slot(struct rxrpc_call_params *p, gfp_t gfp)
+{
+	struct semaphore *limiter = &rxrpc_call_limiter;
+
+	if (p->kernel)
+		limiter = &rxrpc_kernel_call_limiter;
+	if (p->interruptibility == RXRPC_UNINTERRUPTIBLE) {
+		down(limiter);
+		return limiter;
+	}
+	return down_interruptible(limiter) < 0 ? NULL : limiter;
+}
+
+/*
+ * Release a call slot.
+ */
+static void rxrpc_put_call_slot(struct rxrpc_call *call)
+{
+	struct semaphore *limiter = &rxrpc_call_limiter;
+
+	if (test_bit(RXRPC_CALL_KERNEL, &call->flags))
+		limiter = &rxrpc_kernel_call_limiter;
+	up(limiter);
+}
+
+/*
  * Set up a call for the given parameters.
  * - Called with the socket lock held, which it must release.
  * - If it returns a call, the call's lock will need releasing by the caller.
@@ -225,15 +258,21 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
 {
 	struct rxrpc_call *call, *xcall;
 	struct rxrpc_net *rxnet;
+	struct semaphore *limiter;
 	struct rb_node *parent, **pp;
 	const void *here = __builtin_return_address(0);
 	int ret;
 
 	_enter("%p,%lx", rx, p->user_call_ID);
 
+	limiter = rxrpc_get_call_slot(p, gfp);
+	if (!limiter)
+		return ERR_PTR(-ERESTARTSYS);
+
 	call = rxrpc_alloc_client_call(rx, srx, gfp, debug_id);
 	if (IS_ERR(call)) {
 		release_sock(&rx->sk);
+		up(limiter);
 		_leave(" = %ld", PTR_ERR(call));
 		return call;
 	}
@@ -243,6 +282,8 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
 	trace_rxrpc_call(call->debug_id, rxrpc_call_new_client,
 			 atomic_read(&call->usage),
 			 here, (const void *)p->user_call_ID);
+	if (p->kernel)
+		__set_bit(RXRPC_CALL_KERNEL, &call->flags);
 
 	/* We need to protect a partially set up call against the user as we
 	 * will be acting outside the socket lock.
@@ -471,6 +512,8 @@ void rxrpc_release_call(struct rxrpc_sock *rx, struct rxrpc_call *call)
 		BUG();
 	spin_unlock_bh(&call->lock);
 
+	rxrpc_put_call_slot(call);
+
 	del_timer_sync(&call->timer);
 
 	/* Make sure we don't get any more notifications */