We hit the following warning in production
print_req_error: I/O error, dev nbd0, sector 7213934408 flags 80700
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 25 PID: 32407 at lib/refcount.c:190 refcount_sub_and_test_checked+0x53/0x60
Workqueue: knbd-recv recv_work [nbd]
RIP: 0010:refcount_sub_and_test_checked+0x53/0x60
Call Trace:
blk_mq_free_request+0xb7/0xf0
blk_mq_complete_request+0x62/0xf0
recv_work+0x29/0xa1 [nbd]
process_one_work+0x1f5/0x3f0
worker_thread+0x2d/0x3d0
? rescuer_thread+0x340/0x340
kthread+0x111/0x130
? kthread_create_on_node+0x60/0x60
ret_from_fork+0x1f/0x30
---[ end trace b079c3c67f98bb7c ]---
This was preceded by us timing out everything and shutting down the
sockets for the device. The problem is we had a request in the queue at
the same time, so we completed the request twice. This can actually
happen in a lot of cases, we fail to get a ref on our config, we only
have one connection and just error out the command, etc.
Fix this by checking cmd->status in nbd_read_stat. We only change this
under the cmd->lock, so we are safe to check this here and see if we've
already error'ed this command out, which would indicate that we've
completed it as well.
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
drivers/block/nbd.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 8fb8913074b8..e9f5d4e476e7 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -693,6 +693,12 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
ret = -ENOENT;
goto out;
}
+ if (cmd->status != BLK_STS_OK) {
+ dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
+ req);
+ ret = -ENOENT;
+ goto out;
+ }
if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
req);
--
2.21.0
