[PATCH 13/20] nbd: use swapdev hook to make swap deadlock free

[Peter Zijlstra]

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 <[EMAIL PROTECTED]>
Signed-off-by: Daniel Phillips <[EMAIL PROTECTED]>
CC: Pavel Machek <[EMAIL PROTECTED]>
---
 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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