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    SubjectRe: Kernel boot hangs on commit "switch fput to task_work_add"
    On Sat, Jul 14, 2012 at 02:05:10PM +0100, Al Viro wrote:
    > 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]
    > >
    > > 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()..
    >
    > Could you post a stack trace, etc.? I'll try to reproduce that one, obviously,
    > but...

    Yeah, I'm wondering (and will try) if it will help sending SYSRQ into
    kvm guest. It's rather clueless without a back trace..

    Thanks,
    Fengguang


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