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Lockdep issues a circular dependency warning when AFS issues an operation
through AF_RXRPC from a context in which the VFS/VM holds the mmap_sem.
The theory lockdep comes up with is as follows:
(1) If the pagefault handler decides it needs to read pages from AFS, it
calls AFS with mmap_sem held and AFS begins an AF_RXRPC call, but
creating a call requires the socket lock:
mmap_sem must be taken before sk_lock-AF_RXRPC
(2) afs_open_socket() opens an AF_RXRPC socket and binds it. rxrpc_bind()
binds the underlying UDP socket whilst holding its socket lock.
inet_bind() takes its own socket lock:
sk_lock-AF_RXRPC must be taken before sk_lock-AF_INET
(3) Reading from a TCP socket into a userspace buffer might cause a fault
and thus cause the kernel to take the mmap_sem, but the TCP socket is
locked whilst doing this:
sk_lock-AF_INET must be taken before mmap_sem
However, lockdep's theory is wrong in this instance because it deals only
with lock classes and not individual locks. The AF_INET lock in (2) isn't
really equivalent to the AF_INET lock in (3) as the former deals with a
socket entirely internal to the kernel that never sees userspace. This is
a limitation in the design of lockdep.
Fix the general case by:
(1) Double up all the locking keys used in sockets so that one set are
used if the socket is created by userspace and the other set is used
if the socket is created by the kernel.
(2) Store the kern parameter passed to sk_alloc() in a variable in the
sock struct (sk_kern_sock). This informs sock_lock_init(),
sock_init_data() and sk_clone_lock() as to the lock keys to be used.
Note that the child created by sk_clone_lock() inherits the parent's
kern setting.
(3) Add a 'kern' parameter to ->accept() that is analogous to the one
passed in to ->create() that distinguishes whether kernel_accept() or
sys_accept4() was the caller and can be passed to sk_alloc().
Note that a lot of accept functions merely dequeue an already
allocated socket. I haven't touched these as the new socket already
exists before we get the parameter.
Note also that there are a couple of places where I've made the accepted
socket unconditionally kernel-based:
irda_accept()
rds_rcp_accept_one()
tcp_accept_from_sock()
because they follow a sock_create_kern() and accept off of that.
Whilst creating this, I noticed that lustre and ocfs don't create sockets
through sock_create_kern() and thus they aren't marked as for-kernel,
though they appear to be internal. I wonder if these should do that so
that they use the new set of lock keys.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
55 lines
1.8 KiB
C
55 lines
1.8 KiB
C
#ifndef _INET_COMMON_H
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#define _INET_COMMON_H
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extern const struct proto_ops inet_stream_ops;
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extern const struct proto_ops inet_dgram_ops;
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/*
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* INET4 prototypes used by INET6
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*/
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struct msghdr;
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struct sock;
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struct sockaddr;
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struct socket;
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int inet_release(struct socket *sock);
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int inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
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int addr_len, int flags);
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int __inet_stream_connect(struct socket *sock, struct sockaddr *uaddr,
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int addr_len, int flags, int is_sendmsg);
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int inet_dgram_connect(struct socket *sock, struct sockaddr *uaddr,
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int addr_len, int flags);
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int inet_accept(struct socket *sock, struct socket *newsock, int flags,
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bool kern);
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int inet_sendmsg(struct socket *sock, struct msghdr *msg, size_t size);
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ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset,
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size_t size, int flags);
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int inet_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
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int flags);
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int inet_shutdown(struct socket *sock, int how);
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int inet_listen(struct socket *sock, int backlog);
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void inet_sock_destruct(struct sock *sk);
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int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len);
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int inet_getname(struct socket *sock, struct sockaddr *uaddr, int *uaddr_len,
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int peer);
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int inet_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
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int inet_ctl_sock_create(struct sock **sk, unsigned short family,
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unsigned short type, unsigned char protocol,
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struct net *net);
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int inet_recv_error(struct sock *sk, struct msghdr *msg, int len,
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int *addr_len);
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struct sk_buff **inet_gro_receive(struct sk_buff **head, struct sk_buff *skb);
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int inet_gro_complete(struct sk_buff *skb, int nhoff);
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struct sk_buff *inet_gso_segment(struct sk_buff *skb,
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netdev_features_t features);
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static inline void inet_ctl_sock_destroy(struct sock *sk)
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{
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if (sk)
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sock_release(sk->sk_socket);
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}
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#endif
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