[PATCH v2 0/4] nbd: Remove signal usage

[PATCH v2 0/4] nbd: Remove signal usage

[Markus Pargmann]

Hi,

v2 fixes a locking problem with the sock_lock and timers in the first patch.

Best Regards,

Markus

Markus Pargmann (4):
  nbd: Remove signal usage
  nbd: Timeouts are not user requested disconnects
  nbd: Cleanup reset of nbd and bdev after a disconnect
  nbd: Move flag parsing to a function

 drivers/block/nbd.c | 197 +++++++++++++++++++++++++---------------------------
 1 file changed, 96 insertions(+), 101 deletions(-)

-- 
2.6.2

[PATCH v2 1/4] nbd: Remove signal usage

[Markus Pargmann]

As discussed on the mailing list, the usage of signals for timeout
handling has a lot of potential issues. The nbd driver used for some
time signals for timeouts. These signals where able to get the threads
out of the blocking socket operations.

This patch removes all signal usage and uses a socket shutdown instead.
The socket descriptor itself is cleared later when the whole nbd device
is closed.

The tasks_lock is removed as we do not depend on this anymore. Instead
a new lock for the socket is introduced so we can safely work with the
socket in the timeout handler outside of the two main threads.

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
---
 drivers/block/nbd.c | 126 ++++++++++++++++++++--------------------------------
 1 file changed, 48 insertions(+), 78 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b9e4179a950a..88762f640527 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -60,7 +60,8 @@ struct nbd_device {
 	bool disconnect; /* a disconnect has been requested by user */
 
 	struct timer_list timeout_timer;
-	spinlock_t tasks_lock;
+	/* protects initialization and shutdown of the socket */
+	spinlock_t sock_lock;
 	struct task_struct *task_recv;
 	struct task_struct *task_send;
 
@@ -129,13 +130,20 @@ static void nbd_end_request(struct nbd_device *nbd, struct request *req)
  */
 static void sock_shutdown(struct nbd_device *nbd)
 {
-	if (!nbd->sock)
+	spin_lock_irq(&nbd->sock_lock);
+
+	if (!nbd->sock) {
+		spin_unlock_irq(&nbd->sock_lock);
 		return;
+	}
 
 	dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
 	kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
+	sockfd_put(nbd->sock);
 	nbd->sock = NULL;
-	del_timer_sync(&nbd->timeout_timer);
+	spin_unlock_irq(&nbd->sock_lock);
+
+	del_timer(&nbd->timeout_timer);
 }
 
 static void nbd_xmit_timeout(unsigned long arg)
@@ -148,17 +156,15 @@ static void nbd_xmit_timeout(unsigned long arg)
 
 	nbd->disconnect = true;
 
-	spin_lock_irqsave(&nbd->tasks_lock, flags);
+	spin_lock_irqsave(&nbd->sock_lock, flags);
 
-	if (nbd->task_recv)
-		force_sig(SIGKILL, nbd->task_recv);
 
-	if (nbd->task_send)
-		force_sig(SIGKILL, nbd->task_send);
+	if (nbd->sock)
+		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
 
-	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
+	spin_unlock_irqrestore(&nbd->sock_lock, flags);
 
-	dev_err(nbd_to_dev(nbd), "Connection timed out, killed receiver and sender, shutting down connection\n");
+	dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
 }
 
 /*
@@ -171,7 +177,6 @@ static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
 	int result;
 	struct msghdr msg;
 	struct kvec iov;
-	sigset_t blocked, oldset;
 	unsigned long pflags = current->flags;
 
 	if (unlikely(!sock)) {
@@ -181,11 +186,6 @@ static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
 		return -EINVAL;
 	}
 
-	/* Allow interception of SIGKILL only
-	 * Don't allow other signals to interrupt the transmission */
-	siginitsetinv(&blocked, sigmask(SIGKILL));
-	sigprocmask(SIG_SETMASK, &blocked, &oldset);
-
 	current->flags |= PF_MEMALLOC;
 	do {
 		sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
@@ -212,7 +212,6 @@ static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
 		buf += result;
 	} while (size > 0);
 
-	sigprocmask(SIG_SETMASK, &oldset, NULL);
 	tsk_restore_flags(current, pflags, PF_MEMALLOC);
 
 	if (!send && nbd->xmit_timeout)
@@ -406,23 +405,18 @@ static int nbd_thread_recv(struct nbd_device *nbd)
 {
 	struct request *req;
 	int ret;
-	unsigned long flags;
 
 	BUG_ON(nbd->magic != NBD_MAGIC);
 
 	sk_set_memalloc(nbd->sock->sk);
 
-	spin_lock_irqsave(&nbd->tasks_lock, flags);
 	nbd->task_recv = current;
-	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
 
 	ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
 	if (ret) {
 		dev_err(disk_to_dev(nbd->disk), "device_create_file failed!\n");
 
-		spin_lock_irqsave(&nbd->tasks_lock, flags);
 		nbd->task_recv = NULL;
-		spin_unlock_irqrestore(&nbd->tasks_lock, flags);
 
 		return ret;
 	}
@@ -439,19 +433,7 @@ static int nbd_thread_recv(struct nbd_device *nbd)
 
 	device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
 
-	spin_lock_irqsave(&nbd->tasks_lock, flags);
 	nbd->task_recv = NULL;
-	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
-
-	if (signal_pending(current)) {
-		ret = kernel_dequeue_signal(NULL);
-		dev_warn(nbd_to_dev(nbd), "pid %d, %s, got signal %d\n",
-			 task_pid_nr(current), current->comm, ret);
-		mutex_lock(&nbd->tx_lock);
-		sock_shutdown(nbd);
-		mutex_unlock(&nbd->tx_lock);
-		ret = -ETIMEDOUT;
-	}
 
 	return ret;
 }
@@ -544,11 +526,8 @@ static int nbd_thread_send(void *data)
 {
 	struct nbd_device *nbd = data;
 	struct request *req;
-	unsigned long flags;
 
-	spin_lock_irqsave(&nbd->tasks_lock, flags);
 	nbd->task_send = current;
-	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
 
 	set_user_nice(current, MIN_NICE);
 	while (!kthread_should_stop() || !list_empty(&nbd->waiting_queue)) {
@@ -557,17 +536,6 @@ static int nbd_thread_send(void *data)
 					 kthread_should_stop() ||
 					 !list_empty(&nbd->waiting_queue));
 
-		if (signal_pending(current)) {
-			int ret = kernel_dequeue_signal(NULL);
-
-			dev_warn(nbd_to_dev(nbd), "pid %d, %s, got signal %d\n",
-				 task_pid_nr(current), current->comm, ret);
-			mutex_lock(&nbd->tx_lock);
-			sock_shutdown(nbd);
-			mutex_unlock(&nbd->tx_lock);
-			break;
-		}
-
 		/* extract request */
 		if (list_empty(&nbd->waiting_queue))
 			continue;
@@ -582,13 +550,7 @@ static int nbd_thread_send(void *data)
 		nbd_handle_req(nbd, req);
 	}
 
-	spin_lock_irqsave(&nbd->tasks_lock, flags);
 	nbd->task_send = NULL;
-	spin_unlock_irqrestore(&nbd->tasks_lock, flags);
-
-	/* Clear maybe pending signals */
-	if (signal_pending(current))
-		kernel_dequeue_signal(NULL);
 
 	return 0;
 }
@@ -636,6 +598,25 @@ static void nbd_request_handler(struct request_queue *q)
 	}
 }
 
+static int nbd_set_socket(struct nbd_device *nbd, struct socket *sock)
+{
+	int ret = 0;
+
+	spin_lock_irq(&nbd->sock_lock);
+
+	if (nbd->sock) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	nbd->sock = sock;
+
+out:
+	spin_unlock_irq(&nbd->sock_lock);
+
+	return ret;
+}
+
 static int nbd_dev_dbg_init(struct nbd_device *nbd);
 static void nbd_dev_dbg_close(struct nbd_device *nbd);
 
@@ -668,32 +649,26 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		return 0;
 	}
  
-	case NBD_CLEAR_SOCK: {
-		struct socket *sock = nbd->sock;
-		nbd->sock = NULL;
+	case NBD_CLEAR_SOCK:
+		sock_shutdown(nbd);
 		nbd_clear_que(nbd);
 		BUG_ON(!list_empty(&nbd->queue_head));
 		BUG_ON(!list_empty(&nbd->waiting_queue));
 		kill_bdev(bdev);
-		if (sock)
-			sockfd_put(sock);
 		return 0;
-	}
 
 	case NBD_SET_SOCK: {
-		struct socket *sock;
 		int err;
-		if (nbd->sock)
-			return -EBUSY;
-		sock = sockfd_lookup(arg, &err);
-		if (sock) {
-			nbd->sock = sock;
-			if (max_part > 0)
-				bdev->bd_invalidated = 1;
-			nbd->disconnect = false; /* we're connected now */
-			return 0;
-		}
-		return -EINVAL;
+		struct socket *sock = sockfd_lookup(arg, &err);
+
+		if (!sock)
+			return err;
+
+		err = nbd_set_socket(nbd, sock);
+		if (!err && max_part)
+			bdev->bd_invalidated = 1;
+
+		return err;
 	}
 
 	case NBD_SET_BLKSIZE:
@@ -734,7 +709,6 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 
 	case NBD_DO_IT: {
 		struct task_struct *thread;
-		struct socket *sock;
 		int error;
 
 		if (nbd->task_recv)
@@ -769,14 +743,10 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		mutex_lock(&nbd->tx_lock);
 
 		sock_shutdown(nbd);
-		sock = nbd->sock;
-		nbd->sock = NULL;
 		nbd_clear_que(nbd);
 		kill_bdev(bdev);
 		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
 		set_device_ro(bdev, false);
-		if (sock)
-			sockfd_put(sock);
 		nbd->flags = 0;
 		nbd->bytesize = 0;
 		bdev->bd_inode->i_size = 0;
@@ -1043,7 +1013,7 @@ static int __init nbd_init(void)
 		nbd_dev[i].magic = NBD_MAGIC;
 		INIT_LIST_HEAD(&nbd_dev[i].waiting_queue);
 		spin_lock_init(&nbd_dev[i].queue_lock);
-		spin_lock_init(&nbd_dev[i].tasks_lock);
+		spin_lock_init(&nbd_dev[i].sock_lock);
 		INIT_LIST_HEAD(&nbd_dev[i].queue_head);
 		mutex_init(&nbd_dev[i].tx_lock);
 		init_timer(&nbd_dev[i].timeout_timer);
-- 
2.6.2

[PATCH v2 2/4] nbd: Timeouts are not user requested disconnects

[Markus Pargmann]

It may be useful to know in the client that a connection timed out. The
current code returns success for a timeout.

This patch reports the error code -ETIMEDOUT for a timeout.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
---
 drivers/block/nbd.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 88762f640527..0ba3149c48bb 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -57,6 +57,7 @@ struct nbd_device {
 	int blksize;
 	loff_t bytesize;
 	int xmit_timeout;
+	bool timedout;
 	bool disconnect; /* a disconnect has been requested by user */
 
 	struct timer_list timeout_timer;
@@ -154,10 +155,9 @@ static void nbd_xmit_timeout(unsigned long arg)
 	if (list_empty(&nbd->queue_head))
 		return;
 
-	nbd->disconnect = true;
-
 	spin_lock_irqsave(&nbd->sock_lock, flags);
 
+	nbd->timedout = true;
 
 	if (nbd->sock)
 		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
@@ -754,7 +754,10 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		if (max_part > 0)
 			blkdev_reread_part(bdev);
 		if (nbd->disconnect) /* user requested, ignore socket errors */
-			return 0;
+			error = 0;
+		if (nbd->timedout)
+			error = -ETIMEDOUT;
+
 		return error;
 	}
 
-- 
2.6.2

[PATCH v2 3/4] nbd: Cleanup reset of nbd and bdev after a disconnect

[Markus Pargmann]

Group all variables that are reset after a disconnect into reset
functions. This patch adds two of these functions, nbd_reset() and
nbd_bdev_reset().

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
---
 drivers/block/nbd.c | 40 +++++++++++++++++++++++++++++-----------
 1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 0ba3149c48bb..a1fa356e4cbf 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -617,6 +617,30 @@ out:
 	return ret;
 }
 
+/* Reset all properties of an NBD device */
+static void nbd_reset(struct nbd_device *nbd)
+{
+	nbd->disconnect = false;
+	nbd->timedout = false;
+	nbd->blksize = 1024;
+	nbd->bytesize = 0;
+	set_capacity(nbd->disk, 0);
+	nbd->flags = 0;
+	nbd->xmit_timeout = 0;
+	queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
+	del_timer_sync(&nbd->timeout_timer);
+}
+
+static void nbd_bdev_reset(struct block_device *bdev)
+{
+	set_device_ro(bdev, false);
+	bdev->bd_inode->i_size = 0;
+	if (max_part > 0) {
+		blkdev_reread_part(bdev);
+		bdev->bd_invalidated = 1;
+	}
+}
+
 static int nbd_dev_dbg_init(struct nbd_device *nbd);
 static void nbd_dev_dbg_close(struct nbd_device *nbd);
 
@@ -745,19 +769,15 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		sock_shutdown(nbd);
 		nbd_clear_que(nbd);
 		kill_bdev(bdev);
-		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
-		set_device_ro(bdev, false);
-		nbd->flags = 0;
-		nbd->bytesize = 0;
-		bdev->bd_inode->i_size = 0;
-		set_capacity(nbd->disk, 0);
-		if (max_part > 0)
-			blkdev_reread_part(bdev);
+		nbd_bdev_reset(bdev);
+
 		if (nbd->disconnect) /* user requested, ignore socket errors */
 			error = 0;
 		if (nbd->timedout)
 			error = -ETIMEDOUT;
 
+		nbd_reset(nbd);
+
 		return error;
 	}
 
@@ -1024,14 +1044,12 @@ static int __init nbd_init(void)
 		nbd_dev[i].timeout_timer.data = (unsigned long)&nbd_dev[i];
 		init_waitqueue_head(&nbd_dev[i].active_wq);
 		init_waitqueue_head(&nbd_dev[i].waiting_wq);
-		nbd_dev[i].blksize = 1024;
-		nbd_dev[i].bytesize = 0;
 		disk->major = NBD_MAJOR;
 		disk->first_minor = i << part_shift;
 		disk->fops = &nbd_fops;
 		disk->private_data = &nbd_dev[i];
 		sprintf(disk->disk_name, "nbd%d", i);
-		set_capacity(disk, 0);
+		nbd_reset(&nbd_dev[i]);
 		add_disk(disk);
 	}
 
-- 
2.6.2

[PATCH v2 4/4] nbd: Move flag parsing to a function

[Markus Pargmann]

nbd changes properties of the blockdevice depending on flags that were
received. This patch moves this flag parsing into a separate function
nbd_parse_flags().

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
---
 drivers/block/nbd.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index a1fa356e4cbf..81a9be7d176c 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -641,6 +641,18 @@ static void nbd_bdev_reset(struct block_device *bdev)
 	}
 }
 
+static void nbd_parse_flags(struct nbd_device *nbd, struct block_device *bdev)
+{
+	if (nbd->flags & NBD_FLAG_READ_ONLY)
+		set_device_ro(bdev, true);
+	if (nbd->flags & NBD_FLAG_SEND_TRIM)
+		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
+	if (nbd->flags & NBD_FLAG_SEND_FLUSH)
+		blk_queue_flush(nbd->disk->queue, REQ_FLUSH);
+	else
+		blk_queue_flush(nbd->disk->queue, 0);
+}
+
 static int nbd_dev_dbg_init(struct nbd_device *nbd);
 static void nbd_dev_dbg_close(struct nbd_device *nbd);
 
@@ -742,15 +754,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 
 		mutex_unlock(&nbd->tx_lock);
 
-		if (nbd->flags & NBD_FLAG_READ_ONLY)
-			set_device_ro(bdev, true);
-		if (nbd->flags & NBD_FLAG_SEND_TRIM)
-			queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
-				nbd->disk->queue);
-		if (nbd->flags & NBD_FLAG_SEND_FLUSH)
-			blk_queue_flush(nbd->disk->queue, REQ_FLUSH);
-		else
-			blk_queue_flush(nbd->disk->queue, 0);
+		nbd_parse_flags(nbd, bdev);
 
 		thread = kthread_run(nbd_thread_send, nbd, "%s",
 				     nbd_name(nbd));
-- 
2.6.2