Skip to content

Commit

Permalink
af_unix: split 'u->readlock' into two: 'iolock' and 'bindlock'
Browse files Browse the repository at this point in the history 
Right now we use the 'readlock' both for protecting some of the af_unix
IO path and for making the bind be single-threaded.

The two are independent, but using the same lock makes for a nasty
deadlock due to ordering with regards to filesystem locking.  The bind
locking would want to nest outside the VSF pathname locking, but the IO
locking wants to nest inside some of those same locks.

We tried to fix this earlier with commit c845acb ("af_unix: Fix
splice-bind deadlock") which moved the readlock inside the vfs locks,
but that caused problems with overlayfs that will then call back into
filesystem routines that take the lock in the wrong order anyway.

Splitting the locks means that we can go back to having the bind lock be
the outermost lock, and we don't have any deadlocks with lock ordering.

Acked-by: Rainer Weikusat <[email protected]>
Acked-by: Al Viro <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Acked-by: Hannes Frederic Sowa <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
  • Loading branch information
@torvalds @davem330
torvalds authored and davem330 committed Sep 4, 2016
1 parent 38f7bd9 commit 6e1ce3c
Show file tree
Hide file tree
Showing 2 changed files with 24 additions and 23 deletions.
2 changes: 1 addition & 1 deletion include/net/af_unix.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,7 @@ struct unix_sock {
struct sock sk;
struct unix_address *addr;
struct path path;
struct mutex readlock;
struct mutex iolock, bindlock;
struct sock *peer;
struct list_head link;
atomic_long_t inflight;
Expand Down
45 changes: 23 additions & 22 deletions net/unix/af_unix.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -661,11 +661,11 @@ static int unix_set_peek_off(struct sock *sk, int val)
{
struct unix_sock *u = unix_sk(sk);

if (mutex_lock_interruptible(&u->readlock))
if (mutex_lock_interruptible(&u->iolock))
return -EINTR;

sk->sk_peek_off = val;
mutex_unlock(&u->readlock);
mutex_unlock(&u->iolock);

return 0;
}
Expand Down Expand Up @@ -779,7 +779,8 @@ static struct sock *unix_create1(struct net *net, struct socket *sock, int kern)
spin_lock_init(&u->lock);
atomic_long_set(&u->inflight, 0);
INIT_LIST_HEAD(&u->link);
mutex_init(&u->readlock); /* single task reading lock */
mutex_init(&u->iolock); /* single task reading lock */
mutex_init(&u->bindlock); /* single task binding lock */
init_waitqueue_head(&u->peer_wait);
init_waitqueue_func_entry(&u->peer_wake, unix_dgram_peer_wake_relay);
unix_insert_socket(unix_sockets_unbound(sk), sk);
Expand Down Expand Up @@ -848,7 +849,7 @@ static int unix_autobind(struct socket *sock)
int err;
unsigned int retries = 0;

err = mutex_lock_interruptible(&u->readlock);
err = mutex_lock_interruptible(&u->bindlock);
if (err)
return err;

Expand Down Expand Up @@ -895,7 +896,7 @@ static int unix_autobind(struct socket *sock)
spin_unlock(&unix_table_lock);
err = 0;

out: mutex_unlock(&u->readlock);
out: mutex_unlock(&u->bindlock);
return err;
}

Expand Down Expand Up @@ -1009,7 +1010,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
goto out;
addr_len = err;

err = mutex_lock_interruptible(&u->readlock);
err = mutex_lock_interruptible(&u->bindlock);
if (err)
goto out;

Expand Down Expand Up @@ -1063,7 +1064,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
out_unlock:
spin_unlock(&unix_table_lock);
out_up:
mutex_unlock(&u->readlock);
mutex_unlock(&u->bindlock);
out:
return err;
}
Expand Down Expand Up @@ -1955,17 +1956,17 @@ static ssize_t unix_stream_sendpage(struct socket *socket, struct page *page,
if (false) {
alloc_skb:
unix_state_unlock(other);
mutex_unlock(&unix_sk(other)->readlock);
mutex_unlock(&unix_sk(other)->iolock);
newskb = sock_alloc_send_pskb(sk, 0, 0, flags & MSG_DONTWAIT,
&err, 0);
if (!newskb)
goto err;
}

/* we must acquire readlock as we modify already present
/* we must acquire iolock as we modify already present
* skbs in the sk_receive_queue and mess with skb->len
*/
err = mutex_lock_interruptible(&unix_sk(other)->readlock);
err = mutex_lock_interruptible(&unix_sk(other)->iolock);
if (err) {
err = flags & MSG_DONTWAIT ? -EAGAIN : -ERESTARTSYS;
goto err;
Expand Down Expand Up @@ -2032,7 +2033,7 @@ static ssize_t unix_stream_sendpage(struct socket *socket, struct page *page,
}

unix_state_unlock(other);
mutex_unlock(&unix_sk(other)->readlock);
mutex_unlock(&unix_sk(other)->iolock);

other->sk_data_ready(other);
scm_destroy(&scm);
Expand All @@ -2041,7 +2042,7 @@ static ssize_t unix_stream_sendpage(struct socket *socket, struct page *page,
err_state_unlock:
unix_state_unlock(other);
err_unlock:
mutex_unlock(&unix_sk(other)->readlock);
mutex_unlock(&unix_sk(other)->iolock);
err:
kfree_skb(newskb);
if (send_sigpipe && !(flags & MSG_NOSIGNAL))
Expand Down Expand Up @@ -2109,22 +2110,22 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);

do {
mutex_lock(&u->readlock);
mutex_lock(&u->iolock);

skip = sk_peek_offset(sk, flags);
skb = __skb_try_recv_datagram(sk, flags, &peeked, &skip, &err,
&last);
if (skb)
break;

mutex_unlock(&u->readlock);
mutex_unlock(&u->iolock);

if (err != -EAGAIN)
break;
} while (timeo &&
!__skb_wait_for_more_packets(sk, &err, &timeo, last));

if (!skb) { /* implies readlock unlocked */
if (!skb) { /* implies iolock unlocked */
unix_state_lock(sk);
/* Signal EOF on disconnected non-blocking SEQPACKET socket. */
if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN &&
Expand Down Expand Up @@ -2189,7 +2190,7 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,

out_free:
skb_free_datagram(sk, skb);
mutex_unlock(&u->readlock);
mutex_unlock(&u->iolock);
out:
return err;
}
Expand Down Expand Up @@ -2284,7 +2285,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
/* Lock the socket to prevent queue disordering
* while sleeps in memcpy_tomsg
*/
mutex_lock(&u->readlock);
mutex_lock(&u->iolock);

if (flags & MSG_PEEK)
skip = sk_peek_offset(sk, flags);
Expand Down Expand Up @@ -2326,7 +2327,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
break;
}

mutex_unlock(&u->readlock);
mutex_unlock(&u->iolock);

timeo = unix_stream_data_wait(sk, timeo, last,
last_len);
Expand All @@ -2337,7 +2338,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
goto out;
}

mutex_lock(&u->readlock);
mutex_lock(&u->iolock);
goto redo;
unlock:
unix_state_unlock(sk);
Expand Down Expand Up @@ -2440,7 +2441,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state)
}
} while (size);

mutex_unlock(&u->readlock);
mutex_unlock(&u->iolock);
if (state->msg)
scm_recv(sock, state->msg, &scm, flags);
else
Expand Down Expand Up @@ -2481,9 +2482,9 @@ static ssize_t skb_unix_socket_splice(struct sock *sk,
int ret;
struct unix_sock *u = unix_sk(sk);

mutex_unlock(&u->readlock);
mutex_unlock(&u->iolock);
ret = splice_to_pipe(pipe, spd);
mutex_lock(&u->readlock);
mutex_lock(&u->iolock);

return ret;
}
Expand Down

0 comments on commit 6e1ce3c

Please sign in to comment.