Commit 20acbd9a authored Nov 02, 2017 by David Howells

rxrpc: Lock around calling a kernel service Rx notification



Place a spinlock around the invocation of call->notify_rx() for a kernel
service call and lock again when ending the call and replace the
notification pointer with a pointer to a dummy function.

This is required because it's possible for rxrpc_notify_socket() to be
called after the call has been ended by the kernel service if called from
the asynchronous work function rxrpc_process_call().

However, rxrpc_notify_socket() currently only holds the RCU read lock when
invoking ->notify_rx(), which means that the afs_call struct would need to
be disposed of by call_rcu() rather than by kfree().

But we shouldn't see any notifications from a call after calling
rxrpc_kernel_end_call(), so a lock is required in rxrpc code.

Without this, we may see the call wait queue as having a corrupt spinlock:

    BUG: spinlock bad magic on CPU#0, kworker/0:2/1612
    general protection fault: 0000 [#1] SMP
    ...
    Workqueue: krxrpcd rxrpc_process_call
    task: ffff88040b83c400 task.stack: ffff88040adfc000
    RIP: 0010:spin_bug+0x161/0x18f
    RSP: 0018:ffff88040adffcc0 EFLAGS: 00010002
    RAX: 0000000000000032 RBX: 6b6b6b6b6b6b6b6b RCX: ffffffff81ab16cf
    RDX: ffff88041fa14c01 RSI: ffff88041fa0ccb8 RDI: ffff88041fa0ccb8
    RBP: ffff88040adffcd8 R08: 00000000ffffffff R09: 00000000ffffffff
    R10: ffff88040adffc60 R11: 000000000000022c R12: ffff88040aca2208
    R13: ffffffff81a58114 R14: 0000000000000000 R15: 0000000000000000
    ....
    Call Trace:
     do_raw_spin_lock+0x1d/0x89
     _raw_spin_lock_irqsave+0x3d/0x49
     ? __wake_up_common_lock+0x4c/0xa7
     __wake_up_common_lock+0x4c/0xa7
     ? __lock_is_held+0x47/0x7a
     __wake_up+0xe/0x10
     afs_wake_up_call_waiter+0x11b/0x122 [kafs]
     rxrpc_notify_socket+0x12b/0x258
     rxrpc_process_call+0x18e/0x7d0
     process_one_work+0x298/0x4de
     ? rescuer_thread+0x280/0x280
     worker_thread+0x1d1/0x2ae
     ? rescuer_thread+0x280/0x280
     kthread+0x12c/0x134
     ? kthread_create_on_node+0x3a/0x3a
     ret_from_fork+0x27/0x40

In this case, note the corrupt data in EBX.  The address of the offending
afs_call is in R12, plus the offset to the spinlock.

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

parent 2d2faaf0

net/rxrpc/af_rxrpc.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -322,6 +322,14 @@ struct rxrpc_call rxrpc_kernel_begin_call(struct socket sock,
		}
		EXPORT_SYMBOL(rxrpc_kernel_begin_call);

		/*
		* Dummy function used to stop the notifier talking to recvmsg().
		*/
		static void rxrpc_dummy_notify_rx(struct sock sk, struct rxrpc_call rxcall,
		unsigned long call_user_ID)
		{
		}

		/**
		* rxrpc_kernel_end_call - Allow a kernel service to end a call it was using
		* @sock: The socket the call is on
		@@ -336,6 +344,14 @@ void rxrpc_kernel_end_call(struct socket sock, struct rxrpc_call call)

		mutex_lock(&call->user_mutex);
		rxrpc_release_call(rxrpc_sk(sock->sk), call);

		/* Make sure we're not going to call back into a kernel service */
		if (call->notify_rx) {
		spin_lock_bh(&call->notify_lock);
		call->notify_rx = rxrpc_dummy_notify_rx;
		spin_unlock_bh(&call->notify_lock);
		}

		mutex_unlock(&call->user_mutex);
		rxrpc_put_call(call, rxrpc_call_put_kernel);
		}

net/rxrpc/ar-internal.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -525,6 +525,7 @@ struct rxrpc_call {
		unsigned long flags;
		unsigned long events;
		spinlock_t lock;
		spinlock_t notify_lock; /* Kernel notification lock */
		rwlock_t state_lock; /* lock for state transition */
		u32 abort_code; /* Local/remote abort code */
		int error; /* Local error incurred */

net/rxrpc/call_object.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -124,6 +124,7 @@ struct rxrpc_call *rxrpc_alloc_call(gfp_t gfp)
		INIT_LIST_HEAD(&call->sock_link);
		init_waitqueue_head(&call->waitq);
		spin_lock_init(&call->lock);
		spin_lock_init(&call->notify_lock);
		rwlock_init(&call->state_lock);
		atomic_set(&call->usage, 1);
		call->debug_id = atomic_inc_return(&rxrpc_debug_id);

net/rxrpc/recvmsg.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -40,7 +40,9 @@ void rxrpc_notify_socket(struct rxrpc_call *call)
		sk = &rx->sk;
		if (rx && sk->sk_state < RXRPC_CLOSE) {
		if (call->notify_rx) {
		spin_lock_bh(&call->notify_lock);
		call->notify_rx(sk, call, call->user_call_ID);
		spin_unlock_bh(&call->notify_lock);
		} else {
		write_lock_bh(&rx->recvmsg_lock);
		if (list_empty(&call->recvmsg_link)) {

Admin message