linux-kernel - Re: Crash in __wake_up

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Date:	Wed, 20 Apr 2016 11:41:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nikolay Borisov <kernel@...p.com>
Cc:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	SiteGround Operations <operations@...eground.com>
Subject: Re: Crash in __wake_up_common

On Tue, Apr 19, 2016 at 05:37:48PM +0300, Nikolay Borisov wrote:
> 
> ffffffff810e08be points to this line in __wake_up_common:
>         list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
> 
> This is the wait_queue_head_t: 
> 
> crash> struct wait_queue_head_t ffff880438ef52c8
> struct wait_queue_head_t {
>   lock = {
>     {
>       rlock = {
>         raw_lock = {
>           val = {
>             counter = 1
>           }
>         }
>       }
>     }
>   }, 
>   task_list = {
>     next = 0x0, 
>     prev = 0xffff880438ef52d8
>   }
> }
> 
> nr_exclusive seems to be 1, and mode is 3 (TASK_NORMAL). 
> 
> The spl module is coming from zfs(ZoL) but I dunno whether this might 
> be a bug in the scheduler or in the zfs. The line which led to the 
> __wake_up is this: 
> 
> wake_up(&tq->tq_wait_waitq);

Given that the waitqueue code is rather widely used, I suspect this is a
fail in zfs. But given the license issues I'm not going near that code.