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Subject[PATCH 13/20] nbd: use swapdev hook to make swap deadlock free
Date
From
Set SOCK_VMIO on the NBD socket and make sure the request_fn always
runs with PF_MEMALLOC when used as a swapper, this ensures we can
always flush the requests.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Daniel Phillips <phillips@google.com>
CC: Pavel Machek <pavel@ucw.cz>
---
drivers/block/nbd.c | 36 +++++++++++++++++++++++++++++++-----
1 file changed, 31 insertions(+), 5 deletions(-)

Index: linux-2.6/drivers/block/nbd.c
===================================================================
--- linux-2.6.orig/drivers/block/nbd.c 2006-09-07 18:44:12.000000000 +0200
+++ linux-2.6/drivers/block/nbd.c 2006-09-07 18:44:22.000000000 +0200
@@ -139,7 +139,6 @@ static int sock_xmit(struct socket *sock
spin_unlock_irqrestore(&current->sighand->siglock, flags);

do {
- sock->sk->sk_allocation = GFP_NOIO;
iov.iov_base = buf;
iov.iov_len = size;
msg.msg_name = NULL;
@@ -406,10 +405,13 @@ static void nbd_clear_que(struct nbd_dev
static void do_nbd_request(request_queue_t * q)
{
struct request *req;
+ unsigned long pflags = current->flags;
+ struct nbd_device *lo = q->queuedata;
+
+ if (lo->sock && sk_has_vmio(lo->sock->sk))
+ current->flags |= PF_MEMALLOC;

while ((req = elv_next_request(q)) != NULL) {
- struct nbd_device *lo;
-
blkdev_dequeue_request(req);
dprintk(DBG_BLKDEV, "%s: request %p: dequeued (flags=%lx)\n",
req->rq_disk->disk_name, req, req->flags);
@@ -417,8 +419,6 @@ static void do_nbd_request(request_queue
if (!(req->flags & REQ_CMD))
goto error_out;

- lo = req->rq_disk->private_data;
-
BUG_ON(lo->magic != LO_MAGIC);

nbd_cmd(req) = NBD_CMD_READ;
@@ -472,6 +472,7 @@ error_out:
* plug the device to close it.
*/
blk_plug_device(q);
+ current->flags = pflags;
return;
}

@@ -530,6 +531,7 @@ static int nbd_ioctl(struct inode *inode
if (S_ISSOCK(inode->i_mode)) {
lo->file = file;
lo->sock = SOCKET_I(inode);
+ lo->sock->sk->sk_allocation = GFP_NOIO;
error = 0;
} else {
fput(file);
@@ -599,10 +601,33 @@ static int nbd_ioctl(struct inode *inode
return -EINVAL;
}

+static int nbd_swapdev(struct gendisk *disk, int enable)
+{
+ struct nbd_device *lo = disk->private_data;
+
+ if (!lo->sock)
+ return -ENODEV;
+
+ if (enable) {
+ sk_adjust_memalloc(0, TX_RESERVE_PAGES);
+ if (!sk_set_vmio(lo->sock->sk))
+ printk(KERN_WARNING
+ "failed to set SOCK_VMIO on NBD socket\n");
+ } else {
+ if (!sk_clear_vmio(lo->sock->sk))
+ printk(KERN_WARNING
+ "failed to clear SOCK_VMIO on NBD socket\n");
+ sk_adjust_memalloc(0, -TX_RESERVE_PAGES);
+ }
+
+ return 0;
+}
+
static struct block_device_operations nbd_fops =
{
.owner = THIS_MODULE,
.ioctl = nbd_ioctl,
+ .swapdev = nbd_swapdev,
};

/*
@@ -638,6 +663,7 @@ static int __init nbd_init(void)
put_disk(disk);
goto out;
}
+ disk->queue->queuedata = &nbd_dev[i];
blk_queue_max_segment_size(disk->queue, PAGE_SIZE);
blk_queue_max_hw_segments(disk->queue, 1);
blk_queue_max_phys_segments(disk->queue, 1);
--

-
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