linux-kernel - Re: Kernel boot hangs on commit "switch fput to task_work

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Message-ID: <20120714130510.GC31729@ZenIV.linux.org.uk>
Date:	Sat, 14 Jul 2012 14:05:10 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	wfg@...ux.intel.com
Cc:	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Kernel boot hangs on commit "switch fput to task_work_add"

On Tue, Jul 10, 2012 at 10:18:30PM +0800, wfg@...ux.intel.com wrote:
> Hi Al,
> 
> The linux-next kernel reliably hung after this line:
> 
> [    4.846260] debug: unmapping init [mem 0xffff88000182a000-0xffff8800019fffff]
> 
> And it's bisected to commit:
> 
>         commit 4a9ffe81385c2af04f296bea05482f34e02ea10d
>         Author: Al Viro <viro@...iv.linux.org.uk>
>         Date:   Sun Jun 24 09:56:45 2012 +0400
> 
>             switch fput to task_work_add
> 
>             ... and schedule_work() for interrupt/kernel_thread callers
>             (and yes, now it *is* OK to call from interrupt).
> 
> I tried add this debug aid:
> 
> init_post(void):
> +       printk(KERN_WARNING "flush_delayed_fput\n");
>         flush_delayed_fput();
> +       printk(KERN_WARNING "flush_delayed_fput done\n");
> 
> And then it hangs after "flush_delayed_fput done". So it's not directly
> freezing inside flush_delayed_fput()..

Could you post a stack trace, etc.?  I'll try to reproduce that one, obviously,
but...
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