2008-12-18 18:31:29

by Pavel Machek

Subject: nbd: fix locking in case of error

This cleans up error handling some more, and prevents return with lock
held from nbd_handle_req when nbd_send_req() fails. It also switches
calling convention of nbd_send_req from 0 = ok, 1 = failed to 0 /
-errno.

Signed-off-by: Pavel Machek <[email protected]>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index fcefbe4..d36787d 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -280,7 +280,7 @@ static int nbd_send_req(struct nbd_devic
return 0;

error_out:
- return 1;
+ return -EIO;
}

static struct request *nbd_find_request(struct nbd_device *lo,
@@ -467,10 +467,9 @@ static void nbd_handle_req(struct nbd_de

mutex_lock(&lo->tx_lock);
if (unlikely(!lo->sock)) {
- mutex_unlock(&lo->tx_lock);
printk(KERN_ERR "%s: Attempted send on closed socket\n",
lo->disk->disk_name);
- goto error_out;
+ goto error_out_unlock;
}

lo->active_req = req;
@@ -478,7 +477,7 @@ static void nbd_handle_req(struct nbd_de
if (nbd_send_req(lo, req) != 0) {
printk(KERN_ERR "%s: Request send failed\n",
lo->disk->disk_name);
- goto error_out;
+ goto error_out_unlock;
} else {
spin_lock(&lo->queue_lock);
list_add(&req->queuelist, &lo->queue_head);
@@ -491,6 +490,8 @@ static void nbd_handle_req(struct nbd_de

return;

+error_out_unlock:
+ mutex_unlock(&lo->tx_lock);
error_out:
req->errors++;
nbd_end_request(req);
@@ -531,7 +532,7 @@ static int nbd_thread(void *data)
* { printk( "Warning: Ignoring result!\n"); nbd_end_request( req ); }
*/

-static void do_nbd_request(struct request_queue * q)
+static void do_nbd_request(struct request_queue *q)
{
struct request *req;


--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

2008-12-18 19:31:48

by Paul Clements

Subject: Re: nbd: fix locking in case of error

Pavel Machek wrote:
> This cleans up error handling some more, and prevents return with lock
> held from nbd_handle_req when nbd_send_req() fails. It also switches

> static struct request *nbd_find_request(struct nbd_device *lo,
> @@ -467,10 +467,9 @@ static void nbd_handle_req(struct nbd_de
>
> mutex_lock(&lo->tx_lock);
> if (unlikely(!lo->sock)) {
> - mutex_unlock(&lo->tx_lock);
> printk(KERN_ERR "%s: Attempted send on closed socket\n",
> lo->disk->disk_name);
> - goto error_out;
> + goto error_out_unlock;
> }
>
> lo->active_req = req;
> @@ -478,7 +477,7 @@ static void nbd_handle_req(struct nbd_de
> if (nbd_send_req(lo, req) != 0) {
> printk(KERN_ERR "%s: Request send failed\n",
> lo->disk->disk_name);
> - goto error_out;
> + goto error_out_unlock;
> } else {
> spin_lock(&lo->queue_lock);
> list_add(&req->queuelist, &lo->queue_head);
> @@ -491,6 +490,8 @@ static void nbd_handle_req(struct nbd_de
>
> return;
>
> +error_out_unlock:
> + mutex_unlock(&lo->tx_lock);
> error_out:
> req->errors++;
> nbd_end_request(req);

Not sure I see the problem. tx_lock is unlocked in every return path
AFAICS. You introduced the tx_lock problem with the previous patch,
where the second error_out was not correct.

--
Paul