Re: do not allow two nbd-clients at same time

Pavel Machek
2009-01-13T08:25:55Z

On Mon 2009-01-12 08:55:10, Paul Clements wrote:
> Pavel Machek wrote:
>> Two nbd-clients at same time are bad idea, and cause WARN_ON from nbd
>> in 2.6.28-rc7 from sysfs_add_one. This simply prevents that from
>> happening.
>
> Thanks for this. But I think we also need the following:
>
> --- drivers/block/nbd.c 2008-12-24 18:26:37.000000000 -0500
> +++ drivers/block/nbd.c 2009-01-12 08:50:17.000000000 -0500
> @@ -406,6 +406,7 @@ static int nbd_do_it(struct nbd_device *
> ret = sysfs_create_file(&disk_to_dev(lo->disk)->kobj,
> &pid_attr.attr);
> if (ret) {
> printk(KERN_ERR "nbd: sysfs_create_file failed!");
> + lo->pid = 0;
> return ret;
> }
>
>

Yep, thanks.

> To zero out pid in the error case. Otherwise, it looks good.

Ok, new patch below.
Pavel

---
Two nbd-clients at same time are bad idea, and cause WARN_ON from nbd
in 2.6.28-rc7 from sysfs_add_one. This simply prevents that from
happening.

To reproduce:

cat /dev/zero | head -c 10000000 > /tmp/delme.fstest.fs
nbd-server 9100 -l /anyone.can.connect > /tmp/delme.fstest.fs &
sleep 1
nbd-client localhost 9100 /dev/nd0 &
nbd-client localhost 9100 /dev/nd0 &

Signed-off-by: Pavel Machek <pavel@suse.cz>
Acked-by: Paul Clements <paul.clements@steeleye.com>

---
commit 831d1b7c7c5b16b1115d7e08ddf9038704653a03
tree 1ae30466acfb40b88cb7c20613f327c3871274ee
parent 66d8f12491f52e259e42148af099a3fc83425a7b
author Pavel <pavel@amd.ucw.cz> Tue, 13 Jan 2009 09:26:22 +0100
committer Pavel <pavel@amd.ucw.cz> Tue, 13 Jan 2009 09:26:22 +0100

drivers/block/nbd.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 670e89d..caf6458 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -406,6 +406,7 @@ static int nbd_do_it(struct nbd_device *
ret = sysfs_create_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
if (ret) {
printk(KERN_ERR "nbd: sysfs_create_file failed!");
+ lo->pid = 0;
return ret;
}

@@ -413,6 +414,7 @@ static int nbd_do_it(struct nbd_device *
nbd_end_request(req);

sysfs_remove_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
+ lo->pid = 0;
return 0;
}

@@ -646,6 +648,8 @@ static int nbd_ioctl(struct block_device
set_capacity(lo->disk, lo->bytesize >> 9);
return 0;
case NBD_DO_IT:
+ if (lo->pid)
+ return -EBUSY;
if (!lo->file)
return -EINVAL;
thread = kthread_create(nbd_thread, lo, lo->disk->disk_name);