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

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 <a.p.zijlstra@chello.nl>
Signed-off-by: Daniel Phillips <phillips@google.com>
---
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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