From: Paul Clements <paul.clements@steeleye.com>
Here's a patch to fix a race condition in nbd that was causing struct
request corruption (requests were being freed while still in use). This
patch improves on the previous one, which admittedly was a bit dodgy, using
struct request's ref_count field (I should have listened to Jens in the
first place :). This should fix all the corner cases related to struct
request usage/freeing in nbd. My stress tests do a lot better with this
patch applied.
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/block/nbd.c | 39 ++++++++++-----------------------------
1 files changed, 10 insertions(+), 29 deletions(-)
diff -puN drivers/block/nbd.c~nbd-fix-struct-request-race-condition drivers/block/nbd.c
--- 25/drivers/block/nbd.c~nbd-fix-struct-request-race-condition Mon Aug 2 15:59:06 2004
+++ 25-akpm/drivers/block/nbd.c Mon Aug 2 15:59:06 2004
@@ -128,23 +128,11 @@ static void nbd_end_request(struct reque
{
int uptodate = (req->errors == 0) ? 1 : 0;
request_queue_t *q = req->q;
- struct nbd_device *lo = req->rq_disk->private_data;
unsigned long flags;
dprintk(DBG_BLKDEV, "%s: request %p: %s\n", req->rq_disk->disk_name,
req, uptodate? "done": "failed");
- spin_lock(&lo->queue_lock);
- while (req->ref_count > 1) { /* still in send */
- spin_unlock(&lo->queue_lock);
- printk(KERN_DEBUG "%s: request %p still in use (%d), waiting\n",
- lo->disk->disk_name, req, req->ref_count);
- set_current_state(TASK_UNINTERRUPTIBLE);
- schedule_timeout(HZ); /* wait a second */
- spin_lock(&lo->queue_lock);
- }
- spin_unlock(&lo->queue_lock);
-
spin_lock_irqsave(q->queue_lock, flags);
if (!end_that_request_first(req, uptodate, req->nr_sectors)) {
end_that_request_last(req);
@@ -228,7 +216,7 @@ static inline int sock_send_bvec(struct
return result;
}
-void nbd_send_req(struct nbd_device *lo, struct request *req)
+static int nbd_send_req(struct nbd_device *lo, struct request *req)
{
int result, i, flags;
struct nbd_request request;
@@ -288,11 +276,11 @@ void nbd_send_req(struct nbd_device *lo,
}
}
up(&lo->tx_lock);
- return;
+ return 0;
error_out:
up(&lo->tx_lock);
- req->errors++;
+ return 1;
}
static struct request *nbd_find_request(struct nbd_device *lo, char *handle)
@@ -477,26 +465,19 @@ static void do_nbd_request(request_queue
}
list_add(&req->queuelist, &lo->queue_head);
- req->ref_count++; /* make sure req does not get freed */
spin_unlock(&lo->queue_lock);
- nbd_send_req(lo, req);
-
- if (req->errors) {
+ if (nbd_send_req(lo, req) != 0) {
printk(KERN_ERR "%s: Request send failed\n",
lo->disk->disk_name);
- spin_lock(&lo->queue_lock);
- list_del_init(&req->queuelist);
- req->ref_count--;
- spin_unlock(&lo->queue_lock);
- nbd_end_request(req);
- spin_lock_irq(q->queue_lock);
- continue;
+ if (nbd_find_request(lo, (char *)&req) != NULL) {
+ /* we still own req */
+ req->errors++;
+ nbd_end_request(req);
+ } else /* we're racing with nbd_clear_que */
+ printk(KERN_DEBUG "nbd: can't find req\n");
}
- spin_lock(&lo->queue_lock);
- req->ref_count--;
- spin_unlock(&lo->queue_lock);
spin_lock_irq(q->queue_lock);
continue;
_