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NBD: allow hung network I/O to be cancelled
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Allow NBD I/O to be cancelled when a network outage occurs.  Previously, I/O
would just hang, and if enough I/O was hung in nbd, the system (at least
user-level) would completely hang until a TCP timeout (default, 15 minutes)
occurred.

The patch introduces a new ioctl NBD_SET_TIMEOUT that allows a transmit
timeout value (in seconds) to be specified.  Any network send that exceeds the
timeout will be cancelled and the nbd connection will be shut down.  I've
tested with various timeout values and 6 seconds seems to be a good choice for
the timeout.  If the NBD_SET_TIMEOUT ioctl is not called, you get the old (I/O
hang) behavior.

Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Paul Clements authored and Linus Torvalds committed Oct 17, 2007
1 parent 4b86a87 commit 7fdfd40
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Showing 2 changed files with 64 additions and 31 deletions.
93 changes: 62 additions & 31 deletions drivers/block/nbd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -113,12 +113,42 @@ static void nbd_end_request(struct request *req)
spin_unlock_irqrestore(q->queue_lock, flags);
}

static void sock_shutdown(struct nbd_device *lo, int lock)
{
/* Forcibly shutdown the socket causing all listeners
* to error
*
* FIXME: This code is duplicated from sys_shutdown, but
* there should be a more generic interface rather than
* calling socket ops directly here */
if (lock)
mutex_lock(&lo->tx_lock);
if (lo->sock) {
printk(KERN_WARNING "%s: shutting down socket\n",
lo->disk->disk_name);
lo->sock->ops->shutdown(lo->sock, SEND_SHUTDOWN|RCV_SHUTDOWN);
lo->sock = NULL;
}
if (lock)
mutex_unlock(&lo->tx_lock);
}

static void nbd_xmit_timeout(unsigned long arg)
{
struct task_struct *task = (struct task_struct *)arg;

printk(KERN_WARNING "nbd: killing hung xmit (%s, pid: %d)\n",
task->comm, task->pid);
force_sig(SIGKILL, task);
}

/*
* Send or receive packet.
*/
static int sock_xmit(struct socket *sock, int send, void *buf, int size,
static int sock_xmit(struct nbd_device *lo, int send, void *buf, int size,
int msg_flags)
{
struct socket *sock = lo->sock;
int result;
struct msghdr msg;
struct kvec iov;
Expand All @@ -139,9 +169,20 @@ static int sock_xmit(struct socket *sock, int send, void *buf, int size,
msg.msg_controllen = 0;
msg.msg_flags = msg_flags | MSG_NOSIGNAL;

if (send)
if (send) {
struct timer_list ti;

if (lo->xmit_timeout) {
init_timer(&ti);
ti.function = nbd_xmit_timeout;
ti.data = (unsigned long)current;
ti.expires = jiffies + lo->xmit_timeout;
add_timer(&ti);
}
result = kernel_sendmsg(sock, &msg, &iov, 1, size);
else
if (lo->xmit_timeout)
del_timer_sync(&ti);
} else
result = kernel_recvmsg(sock, &msg, &iov, 1, size, 0);

if (signal_pending(current)) {
Expand All @@ -150,6 +191,7 @@ static int sock_xmit(struct socket *sock, int send, void *buf, int size,
current->pid, current->comm,
dequeue_signal_lock(current, &current->blocked, &info));
result = -EINTR;
sock_shutdown(lo, !send);
break;
}

Expand All @@ -167,23 +209,22 @@ static int sock_xmit(struct socket *sock, int send, void *buf, int size,
return result;
}

static inline int sock_send_bvec(struct socket *sock, struct bio_vec *bvec,
static inline int sock_send_bvec(struct nbd_device *lo, struct bio_vec *bvec,
int flags)
{
int result;
void *kaddr = kmap(bvec->bv_page);
result = sock_xmit(sock, 1, kaddr + bvec->bv_offset, bvec->bv_len,
flags);
result = sock_xmit(lo, 1, kaddr + bvec->bv_offset, bvec->bv_len, flags);
kunmap(bvec->bv_page);
return result;
}

/* always call with the tx_lock held */
static int nbd_send_req(struct nbd_device *lo, struct request *req)
{
int result, flags;
struct nbd_request request;
unsigned long size = req->nr_sectors << 9;
struct socket *sock = lo->sock;

request.magic = htonl(NBD_REQUEST_MAGIC);
request.type = htonl(nbd_cmd(req));
Expand All @@ -196,8 +237,8 @@ static int nbd_send_req(struct nbd_device *lo, struct request *req)
nbdcmd_to_ascii(nbd_cmd(req)),
(unsigned long long)req->sector << 9,
req->nr_sectors << 9);
result = sock_xmit(sock, 1, &request, sizeof(request),
(nbd_cmd(req) == NBD_CMD_WRITE)? MSG_MORE: 0);
result = sock_xmit(lo, 1, &request, sizeof(request),
(nbd_cmd(req) == NBD_CMD_WRITE) ? MSG_MORE : 0);
if (result <= 0) {
printk(KERN_ERR "%s: Send control failed (result %d)\n",
lo->disk->disk_name, result);
Expand All @@ -217,7 +258,7 @@ static int nbd_send_req(struct nbd_device *lo, struct request *req)
flags = MSG_MORE;
dprintk(DBG_TX, "%s: request %p: sending %d bytes data\n",
lo->disk->disk_name, req, bvec->bv_len);
result = sock_send_bvec(sock, bvec, flags);
result = sock_send_bvec(lo, bvec, flags);
if (result <= 0) {
printk(KERN_ERR "%s: Send data failed (result %d)\n",
lo->disk->disk_name, result);
Expand Down Expand Up @@ -257,11 +298,11 @@ static struct request *nbd_find_request(struct nbd_device *lo,
return ERR_PTR(err);
}

static inline int sock_recv_bvec(struct socket *sock, struct bio_vec *bvec)
static inline int sock_recv_bvec(struct nbd_device *lo, struct bio_vec *bvec)
{
int result;
void *kaddr = kmap(bvec->bv_page);
result = sock_xmit(sock, 0, kaddr + bvec->bv_offset, bvec->bv_len,
result = sock_xmit(lo, 0, kaddr + bvec->bv_offset, bvec->bv_len,
MSG_WAITALL);
kunmap(bvec->bv_page);
return result;
Expand All @@ -273,10 +314,9 @@ static struct request *nbd_read_stat(struct nbd_device *lo)
int result;
struct nbd_reply reply;
struct request *req;
struct socket *sock = lo->sock;

reply.magic = 0;
result = sock_xmit(sock, 0, &reply, sizeof(reply), MSG_WAITALL);
result = sock_xmit(lo, 0, &reply, sizeof(reply), MSG_WAITALL);
if (result <= 0) {
printk(KERN_ERR "%s: Receive control failed (result %d)\n",
lo->disk->disk_name, result);
Expand Down Expand Up @@ -317,7 +357,7 @@ static struct request *nbd_read_stat(struct nbd_device *lo)
struct bio_vec *bvec;

rq_for_each_segment(bvec, req, iter) {
result = sock_recv_bvec(sock, bvec);
result = sock_recv_bvec(lo, bvec);
if (result <= 0) {
printk(KERN_ERR "%s: Receive data failed (result %d)\n",
lo->disk->disk_name, result);
Expand Down Expand Up @@ -392,6 +432,7 @@ static void nbd_clear_que(struct nbd_device *lo)
}
}


/*
* We always wait for result of write, for now. It would be nice to make it optional
* in future
Expand Down Expand Up @@ -500,7 +541,9 @@ static int nbd_ioctl(struct inode *inode, struct file *file,
sreq.nr_sectors = 0;
if (!lo->sock)
return -EINVAL;
mutex_lock(&lo->tx_lock);
nbd_send_req(lo, &sreq);
mutex_unlock(&lo->tx_lock);
return 0;

case NBD_CLEAR_SOCK:
Expand Down Expand Up @@ -544,6 +587,9 @@ static int nbd_ioctl(struct inode *inode, struct file *file,
set_blocksize(inode->i_bdev, lo->blksize);
set_capacity(lo->disk, lo->bytesize >> 9);
return 0;
case NBD_SET_TIMEOUT:
lo->xmit_timeout = arg * HZ;
return 0;
case NBD_SET_SIZE_BLOCKS:
lo->bytesize = ((u64) arg) * lo->blksize;
inode->i_bdev->bd_inode->i_size = lo->bytesize;
Expand All @@ -556,22 +602,7 @@ static int nbd_ioctl(struct inode *inode, struct file *file,
error = nbd_do_it(lo);
if (error)
return error;
/* on return tidy up in case we have a signal */
/* Forcibly shutdown the socket causing all listeners
* to error
*
* FIXME: This code is duplicated from sys_shutdown, but
* there should be a more generic interface rather than
* calling socket ops directly here */
mutex_lock(&lo->tx_lock);
if (lo->sock) {
printk(KERN_WARNING "%s: shutting down socket\n",
lo->disk->disk_name);
lo->sock->ops->shutdown(lo->sock,
SEND_SHUTDOWN|RCV_SHUTDOWN);
lo->sock = NULL;
}
mutex_unlock(&lo->tx_lock);
sock_shutdown(lo, 1);
file = lo->file;
lo->file = NULL;
nbd_clear_que(lo);
Expand Down
2 changes: 2 additions & 0 deletions include/linux/nbd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#define NBD_PRINT_DEBUG _IO( 0xab, 6 )
#define NBD_SET_SIZE_BLOCKS _IO( 0xab, 7 )
#define NBD_DISCONNECT _IO( 0xab, 8 )
#define NBD_SET_TIMEOUT _IO( 0xab, 9 )

enum {
NBD_CMD_READ = 0,
Expand Down Expand Up @@ -65,6 +66,7 @@ struct nbd_device {
int blksize;
u64 bytesize;
pid_t pid; /* pid of nbd-client, if attached */
int xmit_timeout;
};

#endif
Expand Down

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