On Tue, Jul 10, 2012 at 10:18:30PM +0800, wfg@linux.intel.com wrote:
> Hi Al,
> 
> The linux-next kernel reliably hung after this line:
> 
> [    4.846260] debug: unmapping init [mem 0xffff88000182a000-0xffff8800019fffff]

FYI, in another config (attached), it hangs after:

[    6.803484] debug: unmapping init [mem 0xffffffff81c21000-0xffffffff81cacfff]
modprobe: FATAL: Could not load /lib/modules/3.5.0-rc5-bisect-00086-g4a9ffe8/modules.dep: No such file or directory
^M
[    6.820477] modprobe (462) used greatest stack depth: 5072 bytes left
modprobe: FATAL: Could not load /lib/modules/3.5.0-rc5-bisect-00086-g4a9ffe8/modules.dep: No such file or directory
^M
modprobe: FATAL: Could not load /lib/modules/3.5.0-rc5-bisect-00086-g4a9ffe8/modules.dep: No such file or directory
^M
modprobe: FATAL: Could not load /lib/modules/3.5.0-rc5-bisect-00086-g4a9ffe8/modules.dep: No such file or directory
^M
[    6.851363] 99-trinity (471) used greatest stack depth: 5008 bytes left
modprobe: FATAL: Could not load /lib/modules/3.5.0-rc5-bisect-00086-g4a9ffe8/modules.dep: No such file or directory
^M
modprobe: FATAL: Could not load /lib/modules/3.5.0-rc5-bisect-00086-g4a9ffe8/modules.dep: No such file or directory
^M

Thanks,
Fengguang

> And it's bisected to commit:
> 
>         commit 4a9ffe81385c2af04f296bea05482f34e02ea10d
>         Author: Al Viro <viro@zeniv.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()..
> 
> Thanks,
> Fengguang