[PATCH 3/4] nbd: deadlock prevention for NBD

[Peter Zijlstra]

Use sk_set_vmio() on the nbd socket.

Limit each request to 1 page, so that the request throttling also limits the
number of in-flight pages and force the IO scheduler to NOOP as anything else
doesn't make sense anyway.

Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
Signed-off-by: Daniel Phillips <[EMAIL PROTECTED]>
---
 drivers/block/nbd.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

Index: linux-2.6/drivers/block/nbd.c
===================================================================
--- linux-2.6.orig/drivers/block/nbd.c
+++ linux-2.6/drivers/block/nbd.c
@@ -135,7 +135,6 @@ 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;
@@ -361,8 +360,16 @@ static void nbd_do_it(struct nbd_device 
 
        BUG_ON(lo->magic != LO_MAGIC);
 
+       sk_adjust_memalloc(0, 1);
+       if (sk_set_vmio(lo->sock->sk))
+               printk(KERN_WARNING
+                      "failed to set SOCK_VMIO on NBD socket\n");
+
        while ((req = nbd_read_stat(lo)) != NULL)
                nbd_end_request(req);
+
+       sk_adjust_memalloc(0, -1);
+
        return;
 }
 
@@ -525,6 +533,7 @@ 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);
@@ -628,11 +637,16 @@ static int __init nbd_init(void)
                 * every gendisk to have its very own request_queue struct.
                 * These structs are big so we dynamically allocate them.
                 */
-               disk->queue = blk_init_queue(do_nbd_request, &nbd_lock);
+               disk->queue = blk_init_queue_node_elv(do_nbd_request,
+                               &nbd_lock, -1, "noop");
                if (!disk->queue) {
                        put_disk(disk);
                        goto out;
                }
+               blk_queue_pin_elevator(disk->queue);
+               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);
        }
 
        if (register_blkdev(NBD_MAJOR, "nbd")) {
-
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