linux-kernel - [PATCH v5 2/4] nbd: fix might_sleep warning on socket shutdown.

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Message-Id: <1468660932-6388-2-git-send-email-pranjas@gmail.com>
Date:	Sat, 16 Jul 2016 14:52:12 +0530
From:	Pranay Kr Srivastava <pranjas@...il.com>
To:	mpa@...gutronix.de, nbd-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Cc:	"Pranay Kr. Srivastava" <pranjas@...il.com>
Subject: [PATCH v5 2/4] nbd: fix might_sleep warning on socket shutdown.

From: "Pranay Kr. Srivastava" <pranjas@...il.com>

spinlocked ranges should be small and not contain calls into huge
subfunctions. Fix my mistake and just get the pointer to the socket
instead of doing everything with spinlock held.

Reported-by: Mikulas Patocka <mikulas@...bright.com>
Signed-off-by: Markus Pargmann <mpa@...gutronix.de>

Changelog:
Pranay Kr. Srivastava<pranjas@...il.com>:

1) Use spin_lock instead of irq version for sock_shutdown.

2) Use system work queue to actually trigger the shutdown of
   socket. This solves the issue when kernel_sendmsg is currently
   blocked while a timeout occurs.

v5)
   removed unnecessary code as per review of v4).

Signed-off-by: Pranay Kr Srivastava <pranjas@...il.com>
---
 drivers/block/nbd.c | 53 +++++++++++++++++++++++++++++++----------------------
 1 file changed, 31 insertions(+), 22 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 766c401..4919760 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -39,6 +39,7 @@
 #include <asm/types.h>
 
 #include <linux/nbd.h>
+#include <linux/workqueue.h>
 
 struct nbd_device {
 	u32 flags;
@@ -69,6 +70,10 @@ struct nbd_device {
 #if IS_ENABLED(CONFIG_DEBUG_FS)
 	struct dentry *dbg_dir;
 #endif
+	/*
+	 *This is specifically for calling sock_shutdown, for now.
+	 */
+	struct work_struct ws_shutdown;
 };
 
 #if IS_ENABLED(CONFIG_DEBUG_FS)
@@ -95,6 +100,11 @@ static int max_part;
  */
 static DEFINE_SPINLOCK(nbd_lock);
 
+/*
+ * Shutdown function for nbd_dev work struct.
+ */
+static void nbd_ws_func_shutdown(struct work_struct *);
+
 static inline struct device *nbd_to_dev(struct nbd_device *nbd)
 {
 	return disk_to_dev(nbd->disk);
@@ -172,39 +182,30 @@ static void nbd_end_request(struct nbd_device *nbd, struct request *req)
  */
 static void sock_shutdown(struct nbd_device *nbd)
 {
-	spin_lock_irq(&nbd->sock_lock);
-
-	if (!nbd->sock) {
-		spin_unlock_irq(&nbd->sock_lock);
-		return;
-	}
+	struct socket *sock;
 
-	dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
-	kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
-	sockfd_put(nbd->sock);
+	spin_lock(&nbd->sock_lock);
+	sock = nbd->sock;
 	nbd->sock = NULL;
-	spin_unlock_irq(&nbd->sock_lock);
+	spin_unlock(&nbd->sock_lock);
+
+	if (!sock)
+		return;
 
 	del_timer(&nbd->timeout_timer);
+	dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
+	kernel_sock_shutdown(sock, SHUT_RDWR);
+	sockfd_put(sock);
 }
 
 static void nbd_xmit_timeout(unsigned long arg)
 {
 	struct nbd_device *nbd = (struct nbd_device *)arg;
-	unsigned long flags;
 
 	if (list_empty(&nbd->queue_head))
 		return;
-
-	spin_lock_irqsave(&nbd->sock_lock, flags);
-
 	nbd->timedout = true;
-
-	if (nbd->sock)
-		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
-
-	spin_unlock_irqrestore(&nbd->sock_lock, flags);
-
+	schedule_work(&nbd->ws_shutdown);
 	dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection\n");
 }
 
@@ -663,6 +664,7 @@ static void nbd_reset(struct nbd_device *nbd)
 	set_capacity(nbd->disk, 0);
 	nbd->flags = 0;
 	nbd->xmit_timeout = 0;
+	INIT_WORK(&nbd->ws_shutdown, nbd_ws_func_shutdown);
 	queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
 	del_timer_sync(&nbd->timeout_timer);
 }
@@ -798,10 +800,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		nbd_dev_dbg_close(nbd);
 		kthread_stop(thread);
 
+		sock_shutdown(nbd);
 		mutex_lock(&nbd->tx_lock);
 		nbd->task_recv = NULL;
-
-		sock_shutdown(nbd);
 		nbd_clear_que(nbd);
 		kill_bdev(bdev);
 		nbd_bdev_reset(bdev);
@@ -857,6 +858,14 @@ static const struct block_device_operations nbd_fops = {
 	.compat_ioctl =	nbd_ioctl,
 };
 
+static void nbd_ws_func_shutdown(struct work_struct *ws_nbd)
+{
+	struct nbd_device *nbd_dev = container_of(ws_nbd, struct nbd_device,
+						ws_shutdown);
+
+	sock_shutdown(nbd_dev);
+}
+
 #if IS_ENABLED(CONFIG_DEBUG_FS)
 
 static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
-- 
2.6.2