kernel panic due to a missing work initialization in case of zero

[Engel, Amit]

Hi Hou,
Yes, commit 7b96918a173 (nvmet: avoid queuing keep-alive timer if it is disabled) fixes the panic we hit.

One comment:
It might be more elegant to move 
INIT_DELAYED_WORK(&ctrl->ka_work, nvmet_keep_alive_timer);
>From nvmet_start_keep_alive_timer To nvmet_alloc_ctrl
This way, we will not INIT ka_work each time the keep alive timer is started
(each nvmet_set_feat_kato for example, will start_keep_alive_timer)
IMO it make more sense to INIT_DELAYED_WORK only once (as part of alloc_ctrl)

Let me know what you think and if you want me to provide this minor change

Thanks
Amit

-----Original Message-----
From: Hou Pu <houpu.main at gmail.com> 
Sent: Wednesday, April 21, 2021 5:32 AM
To: Engel, Amit
Cc: linux-nvme at lists.infradead.org; sagi at grimberg.me
Subject: kernel panic due to a missing work initialization in case of zero


[EXTERNAL EMAIL] 

On 4/20/21 11:46, Engel, Amit wrote:
> Hello,
> 
> We hit a kernel panic as a result of the below sequence:
> In the current nvmet implementation, as part of 'nvmet_start_keep_alive_timer'
> nvmet_keep_alive_timer work will be initialized only if kato != 0
> 
> when nvme connect cmd is being executed with a zero kato value 
> 'INIT_DELAYED_WORK(&ctrl->ka_work, nvmet_keep_alive_timer)' will not 
> be called
> 
> once keep alive cmd arrives, we call 'mod_delayed_work' for a work 
> that has not been initialized this will lead to kernel WARNING:
> Apr 20 10:32:59 FNM00190700796-A kernel: WARNING: CPU: 11 PID: 75133 
> at kernel/workqueue.c:1447 __queue_work.cold.55+0xc/0x3c And 
> eventually to soft lockup

Hello Engel,

Could you verify this with latest nvme-5.13 branch? I think this might be the same problem as commit 7b96918a173 (nvmet: avoid queuing keep-alive timer if it is disabled) fixed.

Thanks,
Hou

> 
> A simple fix for this issue (I will post a patch soon) is to 
> initialize the work (as part of 'nvmet_start_keep_alive_timer') even 
> if kato == 0
> 
> Thanks
> Amit E