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nbd: fix circular lock dependency between tx_lock and sk_lock #1018

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nbd: fix circular lock dependency between tx_lock and sk_lock #1018

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31 changes: 30 additions & 1 deletion drivers/block/nbd.c
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,7 @@ struct nbd_sock {
struct socket *sock;
struct mutex tx_lock;
struct request *pending;
struct socket *shutdown_sock;
int sent;
bool dead;
int fallback_index;
Expand Down Expand Up @@ -315,7 +316,14 @@ static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
}
}
if (!nsock->dead) {
kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
/*
* Defer shutdown to after tx_lock is released to avoid
* circular lock dependency (tx_lock -> sk_lock).
* Hold an extra file reference so the socket remains
* valid until the deferred shutdown completes.
*/
nsock->shutdown_sock = nsock->sock;
get_file(nsock->sock->file);
if (atomic_dec_return(&nbd->config->live_connections) == 0) {
if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
&nbd->config->runtime_flags)) {
Expand All @@ -331,6 +339,20 @@ static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
nsock->sent = 0;
}

/*
* Perform deferred socket shutdown outside of tx_lock.
* Uses xchg to guarantee only one caller performs the shutdown.
*/
static void nbd_nsock_deferred_shutdown(struct nbd_sock *nsock)
{
struct socket *sock = xchg(&nsock->shutdown_sock, NULL);

if (sock) {
kernel_sock_shutdown(sock, SHUT_RDWR);
sockfd_put(sock);
}
}

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
{
struct queue_limits lim;
Expand Down Expand Up @@ -410,6 +432,7 @@ static void sock_shutdown(struct nbd_device *nbd)
mutex_lock(&nsock->tx_lock);
nbd_mark_nsock_dead(nbd, nsock, 0);
mutex_unlock(&nsock->tx_lock);
nbd_nsock_deferred_shutdown(nsock);
}
dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
}
Expand Down Expand Up @@ -502,6 +525,7 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
if (cmd->cookie == nsock->cookie)
nbd_mark_nsock_dead(nbd, nsock, 1);
mutex_unlock(&nsock->tx_lock);
nbd_nsock_deferred_shutdown(nsock);
}
nbd_requeue_cmd(cmd);
mutex_unlock(&cmd->lock);
Expand Down Expand Up @@ -836,6 +860,7 @@ static void nbd_pending_cmd_work(struct work_struct *work)
wait_ms *= 2;
}
mutex_unlock(&nsock->tx_lock);
nbd_nsock_deferred_shutdown(nsock);
clear_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
out:
mutex_unlock(&cmd->lock);
Expand Down Expand Up @@ -1020,6 +1045,7 @@ static void recv_work(struct work_struct *work)
mutex_lock(&nsock->tx_lock);
nbd_mark_nsock_dead(nbd, nsock, 1);
mutex_unlock(&nsock->tx_lock);
nbd_nsock_deferred_shutdown(nsock);

atomic_dec(&config->recv_threads);
wake_up(&config->recv_wq);
Expand Down Expand Up @@ -1177,6 +1203,7 @@ static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
ret = nbd_send_cmd(nbd, cmd, index);
out:
mutex_unlock(&nsock->tx_lock);
nbd_nsock_deferred_shutdown(nsock);
nbd_config_put(nbd);
return ret;
}
Expand Down Expand Up @@ -1391,6 +1418,8 @@ static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
args->nsock = nsock;
nsock->cookie++;
mutex_unlock(&nsock->tx_lock);
/* Complete any pending shutdown of the old socket */
nbd_nsock_deferred_shutdown(nsock);
sockfd_put(old);

clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
Expand Down