nbd: Fix hungtask when nbd_config_put
I got follow issue:
[ 247.381177] INFO: task kworker/u10:0:47 blocked for more than 120 seconds.
[ 247.382644] Not tainted 4.19.90-dirty #140
[ 247.383502] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 247.385027] Call Trace:
[ 247.388384] schedule+0xb8/0x3c0
[ 247.388966] schedule_timeout+0x2b4/0x380
[ 247.392815] wait_for_completion+0x367/0x510
[ 247.397713] flush_workqueue+0x32b/0x1340
[ 247.402700] drain_workqueue+0xda/0x3c0
[ 247.403442] destroy_workqueue+0x7b/0x690
[ 247.405014] nbd_config_put.cold+0x2f9/0x5b6
[ 247.405823] recv_work+0x1fd/0x2b0
[ 247.406485] process_one_work+0x70b/0x1610
[ 247.407262] worker_thread+0x5a9/0x1060
[ 247.408699] kthread+0x35e/0x430
[ 247.410918] ret_from_fork+0x1f/0x30
We can reproduce issue as follows:
1. Inject memory fault in nbd_start_device
-1244,10 +1248,18 @@ static int nbd_start_device(struct nbd_device *nbd)
nbd_dev_dbg_init(nbd);
for (i = 0; i < num_connections; i++) {
struct recv_thread_args *args;
-
- args = kzalloc(sizeof(*args), GFP_KERNEL);
+
+ if (i == 1) {
+ args = NULL;
+ printk("%s: inject malloc error\n", __func__);
+ }
+ else
+ args = kzalloc(sizeof(*args), GFP_KERNEL);
2. Inject delay in recv_work
-757,6 +760,8 @@ static void recv_work(struct work_struct *work)
blk_mq_complete_request(blk_mq_rq_from_pdu(cmd));
}
+ printk("%s: comm=%s pid=%d\n", __func__, current->comm, current->pid);
+ mdelay(5 * 1000);
nbd_config_put(nbd);
atomic_dec(&config->recv_threads);
wake_up(&config->recv_wq);
3. Create nbd server
nbd-server 8000 /tmp/disk
4. Create nbd client
nbd-client localhost 8000 /dev/nbd1
Then will trigger above issue.
Reason is when add delay in recv_work, lead to release the last reference
of 'nbd->config_refs'. nbd_config_put will call flush_workqueue to make
all work finish. Obviously, it will lead to deadloop.
To solve this issue, according to Josef's suggestion move 'recv_work'
init from start device to nbd_dev_add, then destroy 'recv_work'when
nbd device teardown.
Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20211102015237.2309763-5-yebin10@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
1 file changed