lkml.org 
[lkml]   [2021]   [Oct]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH -next] nbd: Fix hungtask when nbd_config_put
From
Date


On 2021/10/20 22:04, Josef Bacik wrote:
> On Wed, Oct 20, 2021 at 05:48:30PM +0800, Ye Bin wrote:
>> 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 reprodeuce 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 relase 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, we must ensure 'recv_work' all exit before release
>> the last 'nbd->config_refs' reference count.
>>
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
> This isn't the way to fix this. The crux of the problem is the fact that we
> destroy the recv_workq at config time anyway, since it is tied to the nbd
> device.
>
> Fix this instead by getting rid of that, and have the nbd device teardown the
> recv_workq when we destory the nbd device. Alloc it on device allocation and
> stop alloc'ing it with the config. That way we don't have this weird thing
> where we need recv threads to drop their config before the last thing.
>
> And while you're at it would you fix recv_work() so it doesn't modify config
> after it drops it's reference? Thanks,
>
> Josef
> .
Thank you for your reply, I'll make another patch according to your
suggestion.

\
 
 \ /
  Last update: 2021-10-20 16:24    [W:0.065 / U:0.992 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site